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NEET UG MCQ questions — Physics, Chemistry, Botany & Zoology for medical entrance.

904 Q 4 Subjects 12th (PCB)
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Difficulty: All Easy Medium Hard 61–70 of 904
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Q.61 Medium NEET Chemistry Physical Chemistry
An ideal gas undergoes isothermal compression from 10 L to 5 L at constant temperature. The work done ON the gas is:
A Positive
B Negative
C Zero
D Cannot be determined
Correct Answer:  A. Positive
EXPLANATION

In compression, volume decreases and work is done ON the gas, making w positive (in physics convention). W = -nRT ln(Vf/Vi) where Vf < Vi

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Q.62 Medium NEET Chemistry Physical Chemistry
For a buffer solution containing equal molar amounts of acetic acid and sodium acetate, if Ka = 1.8 × 10⁻⁵, what is the pH?
A 3.74
B 4.74
C 5.74
D 2.74
Correct Answer:  B. 4.74
EXPLANATION

Using Henderson-Hasselbalch equation: pH = pKa = -log(1.8 × 10⁻⁵) ≈ 4.74 (when [acid] = [salt])

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Q.63 Easy NEET Chemistry Physical Chemistry
The number of orbitals in a subshell with l = 2 is:
A 3
B 5
C 7
D 9
Correct Answer:  B. 5
EXPLANATION

For l = 2 (d-subshell), ml values range from -2 to +2, giving 5 orbitals

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Q.64 Easy NEET Chemistry Physical Chemistry
In electrochemistry, the reduction potential of Cu²⁺/Cu is +0.34 V and Zn²⁺/Zn is -0.76 V at 25°C. What is E°cell for Zn-Cu cell?
A 0.42 V
B 1.10 V
C 0.58 V
D -0.42 V
Correct Answer:  B. 1.10 V
EXPLANATION

E°cell = E°cathode - E°anode = 0.34 - (-0.76) = 1.10 V

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Q.65 Easy NEET Chemistry Physical Chemistry
For a first-order reaction with half-life of 69.3 minutes, the rate constant k is:
A 1.0 × 10⁻³ min⁻¹
B 0.693 min⁻¹
C 0.1 min⁻¹
D 10 min⁻¹
Correct Answer:  A. 1.0 × 10⁻³ min⁻¹
EXPLANATION

For first-order reaction: t₁/₂ = 0.693/k, so k = 0.693/69.3 = 1.0 × 10⁻³ min⁻¹

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Q.66 Medium NEET Chemistry Physical Chemistry
Which colligative property depends on the nature of solute as well as its concentration?
A Osmotic pressure
B Relative lowering of vapour pressure
C Elevation of boiling point
D Depression of freezing point in non-electrolytic solutions
Correct Answer:  A. Osmotic pressure
EXPLANATION

Osmotic pressure depends on solute nature because it involves membrane interactions. Other colligative properties depend only on number of solute particles

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Q.67 Easy NEET Chemistry Physical Chemistry
The osmotic pressure of a solution at 27°C containing 0.1 mol of solute in 1 L is approximately:
A 2.46 atm
B 3.69 atm
C 1.84 atm
D 4.92 atm
Correct Answer:  A. 2.46 atm
EXPLANATION

π = nRT/V = (0.1 × 0.0821 × 300)/1 = 2.463 atm

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Q.68 Easy NEET Chemistry Physical Chemistry
For the reaction 2H₂ + O₂ → 2H₂O, ΔH = -572 kJ/mol. How much heat is released when 4 moles of H₂ react?
A 286 kJ
B 572 kJ
C 1144 kJ
D 2288 kJ
Correct Answer:  C. 1144 kJ
EXPLANATION

Given reaction releases 572 kJ for 2 moles of H₂. For 4 moles of H₂, heat released = (572/2) × 4 = 1144 kJ

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Q.69 Easy NEET Chemistry Physical Chemistry
Which of the following exhibits the highest lattice energy?
A NaCl
B MgO
C CaO
D KCl
Correct Answer:  B. MgO
EXPLANATION

MgO has the smallest ionic radii and highest charge density among options, leading to maximum lattice energy (~3850 kJ/mol)

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Q.70 Easy NEET Chemistry Physical Chemistry
At 298 K, the solubility product of AgCl is 1.8 × 10⁻¹⁰. What is the solubility of AgCl in mol/L?
A 1.34 × 10⁻⁵
B 4.24 × 10⁻⁵
C 1.8 × 10⁻¹⁰
D 3.6 × 10⁻¹⁰
Correct Answer:  A. 1.34 × 10⁻⁵
EXPLANATION

For AgCl, Ksp = [Ag⁺][Cl⁻] = s². So s = √(1.8 × 10⁻¹⁰) = 1.34 × 10⁻⁵ mol/L

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