UPSC IAS / IPS - MCQ Practice Questions

Understanding:

We need to identify the correct working principle of a Scanning Electron Microscope (SEM), distinguishing it from related instruments.

Step 1: What SEM does

An SEM scans a focused beam of electrons across the surface of a specimen. When the electron beam interacts with atoms on the surface, it causes the emission of secondary electrons and backscattered electrons. Detectors collect these emissions, and the signal intensity at each point is used to construct a detailed three-dimensional-looking image of the surface morphology.

Step 2: Ruling out the other options

X-ray-based transmission imaging describes an X-ray diffractometer or X-ray imaging system, not an SEM. Visible light with optical lenses describes a conventional light (optical) microscope, limited to about 2000× magnification. A sharp metallic tip and quantum tunneling describes a Scanning Tunneling Microscope (STM), a different instrument capable of imaging individual atoms.

Step 3: Key distinction

SEM is specifically used for surface imaging and can achieve magnifications from about 20× to over 500,000×, with a resolution down to a few nanometres. It does not transmit electrons through the sample (that is the Transmission Electron Microscope, TEM).

Answer:

The SEM works by scanning an electron beam over the sample surface and detecting secondary and backscattered electrons to form a high-resolution surface image.

Quick Tip:

Remember the trio — SEM (surface imaging via secondary electrons), TEM (transmission through thin samples), STM (atomic-scale imaging via quantum tunneling). UPSC often tests these distinctions.

Understanding:

We need to identify the geographic coverage area of India's NavIC (IRNSS) satellite navigation system.

Step 1: NavIC overview

NavIC is an indigenous satellite-based navigation system developed by the Indian Space Research Organisation (ISRO). It consists of a constellation of 7 satellites — 3 in geostationary orbit and 4 in geosynchronous orbit — designed to provide accurate position information in the Indian region.

Step 2: Coverage area

NavIC provides two types of services: the Standard Positioning Service (SPS) for civilian users and the Restricted Service (RS) for strategic users. The system is designed to cover India and a region extending approximately 1500 km beyond its borders, encompassing the primary area of interest for India's strategic and civilian needs.

Step 3: Ruling out other options

A 500 km extension is too narrow and does not match the official ISRO specification. NavIC is a regional system, not continental like an extended GLONASS, nor is it global like the US GPS, Russian GLONASS, European Galileo, or Chinese BeiDou.

Answer:

NavIC covers India and a surrounding region of approximately 1500 km, making it a regional navigation satellite system.

Quick Tip:

NavIC is a frequent UPSC topic. Remember: 7 satellites (3 GEO + 4 GSO), regional coverage of ~1500 km around India, and it operates on L5 and S bands.

Understanding:

We need to correctly identify what CRISPR-Cas9 is and how it functions in genetic engineering.

Step 1: What is CRISPR-Cas9?

CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)-Cas9 is a revolutionary genome-editing technology. It uses a synthetic guide RNA (gRNA) that is designed to match a specific target DNA sequence. The gRNA escorts the Cas9 protein (an endonuclease derived from Streptococcus pyogenes) to the exact location in the genome. Cas9 then makes a double-strand break in the DNA at that precise site, enabling researchers to delete, correct, or insert genetic sequences.

Step 2: Why the other options are wrong

Using restriction enzymes to cut at random locations and religating describes early recombinant DNA technology, not CRISPR. Somatic cell nuclear transfer (SCNT) describes the cloning technique used to create Dolly the sheep. Using Agrobacterium tumefaciens describes the Ti-plasmid method used in plant transgenics, which predates CRISPR.

Step 3: Significance

Jennifer Doudna and Emmanuelle Charpentier were awarded the Nobel Prize in Chemistry in 2020 for developing CRISPR-Cas9, recognising its transformative impact on life sciences.

Answer:

CRISPR-Cas9 is a precision gene-editing tool that uses guide RNA to direct the Cas9 enzyme to a specific DNA location for targeted cutting and editing.

Quick Tip:

The 2020 Nobel Prize in Chemistry was awarded for CRISPR-Cas9 — a high-probability UPSC current affairs-science overlap point.

Understanding:

We need to distinguish between geostationary orbit (GSO) and sun-synchronous orbit (SSO) in terms of altitude, inclination, and application.

Step 1: Geostationary Orbit (GSO)

A geostationary orbit is a circular orbit at an altitude of approximately 35,786 km (often rounded to 36,000 km) above the equator. A satellite in this orbit has an orbital period of exactly 24 hours, matching Earth's rotation. As a result, it appears stationary relative to a fixed point on Earth's surface. It is widely used for communication satellites and meteorological satellites (e.g., INSAT series).

Step 2: Sun-Synchronous Orbit (SSO)

A sun-synchronous orbit is a near-polar, low Earth orbit (typically 600–800 km altitude) with a slight westward inclination (about 97–98°). The orbital plane precesses at a rate that matches Earth's revolution around the Sun (~0.9856° per day). This ensures the satellite always passes over any given location on Earth at the same local solar time, providing consistent lighting conditions — ideal for Earth observation, remote sensing, and weather satellites (e.g., IRS series, Resourcesat).

Step 3: Ruling out wrong options

GSO is not a polar orbit; SSO is not equatorial. Their altitudes differ vastly — GSO at ~36,000 km and SSO at 600–800 km. GSO has a 24-hour period, not 1-hour.

Answer:

GSO keeps a satellite fixed over one equatorial point at ~36,000 km, while SSO is a near-polar low Earth orbit ensuring the same local solar time for each overpass.

Quick Tip:

ISRO's remote sensing satellites (IRS, Resourcesat, Cartosat) use SSO, while communication satellites (INSAT, GSAT) use GSO — a common UPSC pairing.

Understanding:

We need to correctly define dark matter and identify the observational evidence that necessitates its existence.

Step 1: What is dark matter?

Dark matter is a hypothetical component of the universe that does not interact with the electromagnetic field, meaning it does not emit, absorb, or reflect light or any other electromagnetic radiation. It is therefore invisible to telescopes of any wavelength. It is thought to account for approximately 27% of the total mass-energy content of the universe.

Step 2: Primary evidence — galactic rotation curves

In the 1970s, astronomers Vera Rubin and Kent Ford measured the rotational velocities of stars in spiral galaxies. According to Newtonian gravity, stars farther from the galactic centre should orbit more slowly (as planets farther from the Sun orbit more slowly). Instead, the rotation curves were found to be nearly flat — outer stars orbit at roughly the same speed as inner stars. This can only be explained if a large amount of unseen mass (dark matter) is distributed in a halo around and beyond the visible galactic disc.

Step 3: Ruling out wrong options

Black holes involve extreme gravity for known matter and are not 'dark matter' in the cosmological sense. Interstellar dust clouds (dark nebulae) are composed of ordinary (baryonic) matter. Neutrinos are too light to account for the required mass; dark matter has NOT been directly detected at the LHC to date.

Answer:

Dark matter is non-luminous hypothetical matter whose existence is inferred primarily from flat galactic rotation curves that cannot be explained by visible mass alone.

Quick Tip:

Additional evidence for dark matter includes gravitational lensing (bending of light beyond what visible matter can explain) and the Bullet Cluster observation — worth mentioning in a UPSC mains answer.

Understanding:

We need to identify the correct mechanism by which mRNA vaccines work, distinguishing them from other vaccine platforms.

Step 1: How mRNA vaccines work

mRNA (messenger RNA) vaccines contain synthetic mRNA molecules encased in lipid nanoparticles, which facilitate entry into human cells. Once inside, the cell's ribosomes read the mRNA and synthesise the corresponding viral protein — in the case of COVID-19 vaccines (Pfizer-BioNTech and Moderna), this is the spike protein of SARS-CoV-2. The immune system recognises this foreign protein, mounts an immune response, and develops memory cells. The mRNA degrades naturally after a short time and never enters the cell nucleus.

Step 2: Key distinction from other platforms

Traditional live-attenuated vaccines (e.g., MMR) do use weakened live viruses. DNA vaccines and viral vector vaccines (e.g., Covishield) use DNA, but mRNA vaccines do NOT integrate into the host genome — the mRNA never enters the nucleus. Convalescent plasma therapy uses pre-formed antibodies from recovered patients and is a passive immunisation strategy, not a vaccine.

Step 3: Why this matters

mRNA vaccine technology is faster to design and manufacture than traditional platforms, and it has no risk of insertional mutagenesis since the mRNA does not interact with the host DNA.

Answer:

mRNA vaccines deliver synthetic mRNA that instructs the body's own cells to produce a viral protein, triggering an immune response without any live virus or DNA integration.

Quick Tip:

India's home-grown mRNA vaccine candidate is GEMCOVAC-19 developed by Gennova Biopharmaceuticals — a relevant UPSC current affairs point alongside the mechanism.

Understanding:

We need to correctly identify the definition of the Internet of Things (IoT) and distinguish it from related technologies.

Step 1: Defining IoT

The Internet of Things refers to the interconnection of everyday physical devices — from household appliances (smart refrigerators, thermostats) to industrial machinery, vehicles, and wearable health monitors — through the internet. These objects are embedded with sensors, actuators, and communication modules that allow them to collect, transmit, and sometimes act on data autonomously. The key characteristic is machine-to-machine (M2M) communication with minimal human intervention.

Step 2: Applications

IoT has wide applications: smart cities (traffic management, smart grids), precision agriculture (soil sensors, drone monitoring), healthcare (remote patient monitoring), and industrial IoT (predictive maintenance). India's Smart Cities Mission heavily leverages IoT.

Step 3: Ruling out wrong options

Connecting computers for shared processing power describes distributed computing or grid computing, not IoT. Encryption protocols describe technologies like TLS/SSL. Immersive digital environments with headsets describe virtual reality (VR) or the metaverse — distinct from IoT.

Answer:

IoT is the network of internet-connected physical devices that collect and exchange data autonomously, enabling smart automation across sectors.

Quick Tip:

For UPSC, link IoT with India's policy initiatives: Smart Cities Mission, Digital India, and the National IoT Policy 2023 draft — these make for strong Mains answers.

Understanding:

We need to correctly define quantum entanglement and identify its role in quantum communication technologies.

Step 1: What is quantum entanglement?

Quantum entanglement is a phenomenon in quantum mechanics where two or more particles (e.g., photons or electrons) are generated or interact in such a way that the quantum state of each particle cannot be described independently of the others, even when separated by large distances. When a measurement is made on one particle, the corresponding state of its entangled partner is instantaneously determined.

Step 2: Does entanglement allow faster-than-light communication?

No. While the correlation appears instantaneously, no usable information can be transmitted faster than light through entanglement. The outcomes of measurements are random, so one party cannot control what the other receives — this is the 'no-communication theorem'. Entanglement is therefore NOT a method for faster-than-light data transmission.

Step 3: Role in Quantum Key Distribution (QKD)

Entanglement is central to quantum cryptography and QKD (e.g., the Ekert protocol). Any eavesdropping on an entangled pair disturbs the quantum states in a detectable way, providing theoretically unbreakable encryption. India's ISRO successfully demonstrated a quantum entanglement-based communication experiment in 2022.

Step 4: Ruling out other options

Superposition of a single particle (not a pair) describes the basic qubit property, not entanglement. The double-slit experiment demonstrates wave-particle duality but is not entanglement.

Answer:

Quantum entanglement describes correlated particle pairs whose states are linked regardless of separation, forming the basis of quantum key distribution for secure communication.

Quick Tip:

India's National Quantum Mission (NQM), approved in 2023, specifically targets quantum communication and QKD — directly relevant to UPSC Science & Technology current affairs.

Understanding:

We need to identify the correct factual statement about ISRO's Chandrayaan-3 mission from the given options.

Step 1: Key facts about Chandrayaan-3

Chandrayaan-3 was launched on 14 July 2023 by the LVM3-M4 (GSLV Mk III) rocket from Sriharikota. It comprised a Propulsion Module, Vikram lander, and Pragyan rover (no separate orbiter). On 23 August 2023, Vikram successfully soft-landed near the lunar south pole (approximately 69° S latitude), a region no country had previously reached. This made India the first nation to land near the lunar south pole and the fourth country overall to achieve a soft landing on the Moon (after USSR, USA, and China).

Step 2: Evaluating each option

Option A is correct in all respects: the date (23 August 2023), location (lunar south pole), and India's distinction (first near south pole, fourth overall).

Option B is incorrect: Chandrayaan-2 (2019) was India's first landing attempt (it crashed); Chandrayaan-3 had no separate orbiter — the Propulsion Module served that role.

Option C is partially correct regarding the rocket (LVM3/GSLV Mk III) but incorrect about the landing site — it landed near the south pole, not the equatorial region.

Option D is incorrect: the Pragyan rover detected sulfur and other elements via its LIBS and RAMBHA instruments but did not 'discover water ice directly on the surface for the first time'.

Answer:

Chandrayaan-3's Vikram lander soft-landed near the lunar south pole on 23 August 2023, making India the first country to land in that region and the fourth to achieve a lunar soft landing.

Quick Tip:

Remember: Chandrayaan-1 (2008) — orbiter + impactor, discovered water molecules; Chandrayaan-2 (2019) — orbiter succeeded, lander crashed; Chandrayaan-3 (2023) — full success near south pole.

Understanding:

We need to correctly describe 5G technology, its frequency bands, and how it differs from 4G LTE.

Step 1: What is 5G?

5G (Fifth Generation) is the latest standard in mobile telecommunications, succeeding 4G LTE. It offers peak data speeds theoretically up to 20 Gbps, ultra-low latency (as low as 1 millisecond), and the ability to connect a massive number of devices simultaneously — enabling applications like autonomous vehicles, smart factories, telemedicine, and IoT.

Step 2: Frequency bands

5G operates across three spectrum ranges:

4G LTE primarily used sub-3 GHz bands (700 MHz, 1800 MHz, 2100 MHz, 2300 MHz) and did not use mmWave frequencies.

Step 3: Ruling out wrong options

5G is not satellite-based (that describes LEO broadband like Starlink). 5G is not limited to 700 MHz; that is one of its low-band options. 5G uses radio waves, not infrared.

Answer:

5G uses sub-6 GHz bands for broad coverage and mmWave bands (24–100 GHz) for ultra-high-speed dense deployments, delivering far greater speeds and lower latency than 4G.

Quick Tip:

India auctioned 5G spectrum in August 2022; Airtel and Jio launched commercial 5G services in October 2022. The 3.5 GHz mid-band is the workhorse of India's 5G deployment.

Understanding:

We need to correctly distinguish between Artificial Intelligence (AI) and Machine Learning (ML) in terms of their scope and relationship.

Step 1: Artificial Intelligence (AI)

AI is the overarching discipline in computer science aimed at creating machines or systems that can perform tasks that typically require human intelligence. These tasks include reasoning, problem-solving, understanding natural language, visual perception, and decision-making. AI encompasses rule-based expert systems, search algorithms, robotics, natural language processing, and machine learning.

Step 2: Machine Learning (ML)

ML is a subset of AI. Rather than being explicitly programmed with rules, ML systems use statistical algorithms to learn patterns from large datasets and improve their performance over time with experience. Examples include image recognition, recommendation engines, and spam filters.

Step 3: The hierarchy

The correct conceptual hierarchy is: AI (broadest) → Machine Learning (subset of AI) → Deep Learning (subset of ML, using neural networks). This directly confirms Option A.

Step 4: Ruling out wrong options

ML is NOT broader than AI — this is a classic reversal error. AI and ML are not synonymous; a simple calculation program is not AI. AI is not hardware; GPUs/TPUs are physical accelerators used to run AI/ML algorithms.

Answer:

AI is the broad field of creating intelligent machines; ML is a subset of AI where systems learn autonomously from data.

Quick Tip:

For UPSC, remember the hierarchy: AI → ML → Deep Learning → Neural Networks. India's National Strategy for Artificial Intelligence (NITI Aayog, 2018) is also examinable context.

Understanding:

We need to identify the correct objective of the Government of India's Genome India Project.

Step 1: About the Genome India Project

The Genome India Project (GIP) was launched in January 2020 under the Department of Biotechnology (DBT), Government of India, as a consortium of 20 leading Indian research institutions. The project aims to collect whole-genome sequences from approximately 10,000 individuals representing the vast genetic diversity of India — covering different ethnic groups, linguistic communities, and geographic regions.

Step 2: Purpose and significance

India's population carries unique genetic variants due to its historically endogamous communities and diverse ancestry. Building a comprehensive Indian genomic reference database will:

Step 3: Ruling out wrong options

The project deals with human genomes, not crop genomes or plant species. Microbiome mapping is a separate field (metagenomics). Conservation genomics for endangered species is done under separate biodiversity programmes.

Answer:

The Genome India Project aims to sequence the genomes of 10,000 Indians from diverse backgrounds to build a reference database for health research and personalised medicine.

Quick Tip:

This project is India's equivalent of efforts like the UK Biobank or the US All of Us programme. It is directly relevant to India's Precision Medicine and Biotechnology policy — a strong UPSC GS-III point.

Understanding:

We need to correctly describe the electrochemical working principle of a lithium-ion (Li-ion) battery.

Step 1: Structure of a Li-ion battery

A lithium-ion battery has three main components:

Step 2: Discharge process

During discharge (powering a device), lithium ions (${\text{Li}}^{+}$) de-intercalate from the graphite anode, travel through the electrolyte, and intercalate into the cathode. Simultaneously, electrons flow from the anode to the cathode through the external circuit, constituting the usable electric current.

Step 3: Charging process

During charging, an external voltage reverses the process — lithium ions move back from the cathode to the anode, and electrons flow in the opposite direction through the external circuit.

Step 4: Ruling out wrong options

The hydrogen-oxygen reaction describes a fuel cell (e.g., used in FCEV like Toyota Mirai), not a Li-ion battery. Nuclear decay powers radioisotope thermoelectric generators (RTGs), not consumer batteries. Li-ion batteries are rechargeable; lithium does not permanently dissolve — it reversibly intercalates.

Answer:

In a Li-ion battery, lithium ions shuttle between graphite anode and lithium metal oxide cathode through the electrolyte, while electrons flow through the external circuit; the reaction is fully reversible.

Quick Tip:

The 2019 Nobel Prize in Chemistry was awarded to John Goodenough, M. Stanley Whittingham, and Akira Yoshino for the development of lithium-ion batteries — a useful fact for UPSC.

Understanding:

We need to correctly define hypersonic missiles, their key characteristics, and identify which country first operationally deployed them.

Step 1: Defining hypersonic missiles

Hypersonic weapons are those that travel at Mach 5 or faster (i.e., five or more times the speed of sound, or roughly 6,000 km/h and above at sea level). There are two main types:

Step 2: What makes them difficult to intercept

Unlike traditional ballistic missiles that follow predictable parabolic trajectories (which existing missile defence systems are designed to intercept), hypersonic weapons can manoeuvre laterally and vertically during flight, fly at lower altitudes, and change their intended target, greatly reducing the effectiveness of current missile defence systems.

Step 3: First operational deployment

Russia declared its Avangard hypersonic glide vehicle system operational in December 2019, making it the first country to operationally deploy a hypersonic weapon. Russia's Kinzhal air-launched hypersonic missile was also declared operational in 2017–2018. China and the USA are in advanced stages of development and testing.

Step 4: India's context

India is developing BrahMos-II (a hypersonic cruise missile) jointly with Russia, as well as indigenous HSTDV (Hypersonic Technology Demonstrator Vehicle) tested by DRDO.

Answer:

Hypersonic missiles exceed Mach 5 and manoeuvre in flight; Russia was first to operationally deploy one with the Avangard HGV system in 2019.

Quick Tip:

For UPSC Mains, the strategic significance of hypersonic weapons lies in their ability to defeat current ABM (Anti-Ballistic Missile) systems, shifting the global nuclear deterrence calculus.

Understanding:

We need to correctly describe blockchain technology and identify the specific feature that guarantees its data integrity.

Step 1: What is blockchain?

A blockchain is a distributed ledger technology (DLT) where data is organised into 'blocks', and each block is cryptographically linked to the one before it. The ledger is maintained simultaneously across a network of computers (nodes) rather than at a single central location. This decentralisation means no single entity controls the data.

Step 2: How data integrity is ensured

Each block contains:

Because each block's hash is included in the next block, altering any historical record changes that block's hash, which then invalidates the hash stored in the next block, propagating through the entire chain. To falsify a record, an attacker would need to recompute and update every subsequent block faster than the entire honest network — computationally infeasible in a large network.

Step 3: Ruling out wrong options

Blockchain is decentralised, not managed by a single authority — that describes a traditional database. Cloud storage with a private key describes encrypted cloud services (e.g., Dropbox with encryption), not blockchain. BitTorrent-style file sharing describes P2P file transfer protocols, fundamentally different from a ledger.

Answer:

Blockchain uses cryptographically linked blocks in a decentralised network; each block's hash of the prior block makes tampering computationally infeasible.

Quick Tip:

India's use of blockchain: NITI Aayog's IndiaChain project, land records management in states like Andhra Pradesh and Telangana, and the RBI's exploration of a Central Bank Digital Currency (CBDC) e-Rupee all use blockchain principles.

Understanding:

We need to correctly identify the orbital location and primary objectives of ISRO's Aditya-L1 solar mission.

Step 1: What is Aditya-L1?

Aditya-L1 is India's first dedicated solar space observatory, launched on 2 September 2023 by the PSLV-C57 rocket from Sriharikota. After a journey of approximately 110 days, it was inserted into a halo orbit around the Sun-Earth Lagrange Point 1 (L1) on 6 January 2024.

Step 2: Why the L1 point?

The L1 point is located approximately 1.5 million km from Earth in the direction of the Sun (about 1% of the Earth-Sun distance). At this gravitational balance point between the Sun and Earth, the spacecraft can maintain a stable halo orbit. The key advantage is that the spacecraft has a continuous, uninterrupted view of the Sun — it never experiences an eclipse or occultation — enabling round-the-clock solar observation.

Step 3: Scientific payloads and objectives

Aditya-L1 carries 7 payloads, including VELC (Visible Emission Line Coronagraph), SUIT (Solar Ultraviolet Imaging Telescope), and ASPEX (Aditya Solar wind Particle Experiment). The primary objectives are:

Step 4: Ruling out wrong options

L4 is the Trojan point (60° ahead), not where Aditya-L1 is. It is not in low Earth orbit (that would severely limit solar observation time). The Earth-Moon L2 point is about 65,000 km behind the Moon, far from the Sun, and unsuitable for solar observation.

Answer:

Aditya-L1 is positioned in a halo orbit at the Sun-Earth L1 point (~1.5 million km from Earth) for continuous solar observation, studying the corona, solar wind, and magnetic field.

Quick Tip:

Other missions at Sun-Earth L1 include NASA/ESA's SOHO and NASA's ACE. The L2 point (opposite side from Sun) is where the James Webb Space Telescope (JWST) operates — a common UPSC confusion point.

Understanding:

We need to correctly define nanotechnology, identify its scale, and identify the primary Indian government body responsible for its promotion.

Step 1: What is nanotechnology?

Nanotechnology is the science, engineering, and application of materials and devices with structures and components at the nanoscale — typically 1 to 100 nanometres (nm). At this scale, materials exhibit novel properties due to quantum mechanical effects and an extremely high surface-area-to-volume ratio, differing significantly from their bulk-material counterparts. Applications span medicine (targeted drug delivery), electronics (transistors, quantum dots), energy (improved solar cells and batteries), textiles, and water purification.

Step 2: Scale clarification

$1\text{ nm}=10^{-9}\text{ m}$, which is about 10 times the diameter of a hydrogen atom. This is the nanometre scale, not the micrometre ($10^{-6}$ m) scale, nor the femtometre ($10^{-15}$ m) scale of subatomic particles.

Step 3: India's Nano Mission

The Government of India launched the 'Nano Mission' in 2007 under the Department of Science and Technology (DST). It funds basic research, infrastructure creation (Nanoscience and Nanotechnology Initiative, NSTI), and application development in nanotechnology across Indian institutions.

Step 4: Ruling out wrong options

Micrometres describe conventional microfabrication, not nanotechnology. Nanobots are one application of nanotechnology, not its definition. Femtometre scales describe nuclear physics, governed by DAE — separate from nanotechnology.

Answer:

Nanotechnology operates at 1–100 nm, exploiting quantum and surface effects; India's DST leads its promotion through the Nano Mission.

Quick Tip:

For UPSC, remember: $1\text{ nm}=10^{-9}\text{ m}$. Nano Mission (DST, 2007) is distinct from the National Biopharma Mission (DBT) — a subtle but examinable distinction.

Understanding:

We need to correctly distinguish between nuclear fission and nuclear fusion in terms of their mechanisms, energy output, and applications.

Step 1: Nuclear fission

Fission is the process in which a heavy atomic nucleus (such as ${}_{92}^{235}\text{U}$ or ${}_{94}^{239}\text{Pu}$) absorbs a neutron and becomes unstable, splitting into two smaller (daughter) nuclei plus additional neutrons and a large amount of energy. The released neutrons can trigger further fission reactions, creating a chain reaction. This is the basis of conventional nuclear reactors and atomic bombs (fission bombs).

Step 2: Nuclear fusion

Fusion is the process in which two light nuclei, such as deuterium (${}_1^2\text{H}$) and tritium (${}_1^3\text{H}$), are forced together at extremely high temperatures and pressures to form a heavier nucleus (helium-4) plus a neutron and a large amount of energy:

Fusion releases significantly more energy per unit mass than fission. It is the process that powers stars (including the Sun) and is the basis of thermonuclear (hydrogen) bombs. Controlled fusion for civilian power generation is still under research (e.g., ITER project).

Step 3: Ruling out wrong options

The definitions in Option B are reversed. Option C reverses the weapon applications — hydrogen bombs use fusion (triggered by fission), while atomic bombs use fission alone. Option D is incorrect; fusion releases far more energy per unit mass than fission.

Answer:

Fission splits heavy nuclei (U-235, Pu-239) and powers reactors and atomic bombs; fusion combines light nuclei (D+T) and powers the Sun and hydrogen bombs, releasing more energy per unit mass.

Quick Tip:

India's nuclear programme uses both: PHWR reactors (fission, using heavy water with natural uranium) for civilian power, and India is a partner in the ITER fusion project. India also plans to use thorium-based fuel cycles in future fission reactors.

Understanding:

We need to correctly define gene therapy and verify a real clinical example of its application.

Step 1: What is gene therapy?

Gene therapy is a medical technique that modifies the genetic material inside a patient's cells to treat, prevent, or cure a disease. There are three broad approaches:

Gene therapy can be ex vivo (cells modified outside the body, then returned) or in vivo (gene delivery directly into the body).

Step 2: Real example — Leber Congenital Amaurosis (LCA)

Luxturna (voretigene neparvovec), approved by the US FDA in 2017, was the first directly administered in vivo gene therapy approved for a genetic disease. It treats LCA type 10, a form of hereditary retinal dystrophy caused by mutations in the RPE65 gene. A functional copy of RPE65 is delivered into retinal cells using an adeno-associated virus (AAV) vector, restoring vision. This is a medically verified example of gene therapy.

Step 3: Ruling out wrong options

Transplanting genetically engineered animal organs into humans describes xenotransplantation (a separate field). Using CRISPR exclusively for 'designer babies' is an ethical misuse, not the definition of gene therapy as a medical treatment. Radiation destroys DNA rather than replacing genes — this is not gene therapy; it more closely (incorrectly) describes myeloablative conditioning before bone marrow transplant.

Answer:

Gene therapy modifies genetic material in cells to treat disease; Luxturna delivering a functional RPE65 gene for hereditary blindness is a landmark approved example.

Quick Tip:

India's Department of Biotechnology (DBT) and CDSCO are developing regulatory frameworks for gene and cell therapies. The first human gene therapy trial globally was conducted by French Anderson in 1990 for ADA-SCID (a severe combined immunodeficiency) — worth knowing for UPSC.

Understanding:

We need to correctly describe the key provisions of India's Digital Personal Data Protection Act, 2023.

Step 1: Background

The DPDP Act, 2023 was passed by the Indian Parliament and received Presidential assent on 11 August 2023. It is India's first comprehensive data protection law, replacing the fragmented data privacy provisions under the IT Act, 2000. It is modelled on global frameworks like the EU's General Data Protection Regulation (GDPR).

Step 2: Key provisions

Step 3: Ruling out wrong options

The Act does not restrict AI. It does not prohibit all cross-border data flows — it permits transfers to notified countries. It applies to both government and private entities. It does not mandate exclusive storage on government servers.

Answer:

The DPDP Act, 2023 creates a legal framework for data processing, grants individuals rights over their data, and establishes the Data Protection Board for enforcement.

Quick Tip:

The Justice B.N. Srikrishna Committee (2018) report 'A Free and Fair Digital Economy' and the Personal Data Protection Bill went through multiple revisions before the final DPDP Act 2023 was enacted — the legislative journey is a UPSC-relevant background.