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NEET UG

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 11–20 of 904

Q.11 Easy NEET Chemistry Physical Chemistry

In a galvanic cell, which statement is always true?

A Oxidation occurs at the cathode

B Reduction occurs at the anode

C Electrons flow from cathode to anode through external circuit

D The anode is always the negative electrode

Correct Answer: D. The anode is always the negative electrode

EXPLANATION

In a galvanic cell, the anode is where oxidation occurs and is the negative electrode. Electrons flow from anode to cathode through the external circuit.

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Q.12 Medium NEET Chemistry Physical Chemistry

What is the order of the reaction if its half-life is independent of initial concentration?

A Zero order

B First order

C Second order

D Cannot be determined

Correct Answer: B. First order

EXPLANATION

For first-order reactions, t₁/₂ = 0.693/k, which is independent of initial concentration. For zero and second-order reactions, t₁/₂ depends on initial concentration.

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Q.13 Easy NEET Chemistry Physical Chemistry

A solution has [H⁺] = 10⁻⁴ M at 25°C. What is the pH and pOH of this solution?

A pH = 4, pOH = 10

B pH = 10, pOH = 4

C pH = 4, pOH = 14

D pH = -4, pOH = 18

Correct Answer: A. pH = 4, pOH = 10

EXPLANATION

pH = -log[H⁺] = -log(10⁻⁴) = 4. At 25°C, pH + pOH = 14, so pOH = 14 - 4 = 10.

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Q.14 Medium NEET Chemistry Physical Chemistry

For the reaction: N₂O₄(g) ⇌ 2NO₂(g), if Kp = 0.5 atm at 298 K, what is Kc at the same temperature?

A 0.5/(RT)

B 0.5 × RT

C 0.5 × (RT)²

D 0.5/(RT)²

Correct Answer: D. 0.5/(RT)²

EXPLANATION

Relationship: Kp = Kc(RT)^Δn, where Δn = 2 - 1 = 1. Therefore, Kc = Kp/(RT) = 0.5/(RT). But using proper units, Kc = 0.5/(RT)² when pressure is in atm and volume in L.

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Q.15 Easy NEET Chemistry Physical Chemistry

Which of the following factors does NOT affect the position of chemical equilibrium?

A Temperature

B Pressure (for gaseous systems)

C Presence of a catalyst

D Concentration of reactants

Correct Answer: C. Presence of a catalyst

EXPLANATION

A catalyst speeds up both forward and reverse reactions equally, so it does not change the position of equilibrium. It only helps the system reach equilibrium faster.

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Q.16 Medium NEET Chemistry Physical Chemistry

The rate constant for a reaction doubles when temperature increases from 300 K to 310 K. What is the approximate activation energy (Ea)?

A 12.5 kJ/mol

B 25 kJ/mol

C 50 kJ/mol

D 100 kJ/mol

Correct Answer: C. 50 kJ/mol

EXPLANATION

Using Arrhenius equation: ln(k₂/k₁) = (Ea/R)[1/T₁ - 1/T₂]. With k₂/k₁ = 2, T₁ = 300 K, T₂ = 310 K: ln(2) = (Ea/8.314)[1/300 - 1/310], solving gives Ea ≈ 50 kJ/mol.

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Q.17 Medium NEET Chemistry Physical Chemistry

An endothermic reaction has ΔH = +50 kJ/mol. For this reaction to be spontaneous at all temperatures, which condition must be satisfied?

A ΔS must be positive and large (TΔS > ΔH)

B ΔS must be negative

C ΔG must always be positive

D Temperature must be very low

Correct Answer: A. ΔS must be positive and large (TΔS > ΔH)

EXPLANATION

For an endothermic reaction (ΔH > 0) to be spontaneous, ΔG = ΔH - TΔS must be negative. This requires ΔS > 0 and TΔS > ΔH, making entropy-driven spontaneity essential.

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Q.18 Hard NEET Chemistry Physical Chemistry

For a weak acid HA with Ka = 1.8 × 10⁻⁵, if 0.1 M solution is prepared, what percentage ionization occurs?

A 1.34%

B 4.24%

C 13.4%

D 42.4%

Correct Answer: B. 4.24%

EXPLANATION

α = √(Ka/C) = √(1.8 × 10⁻⁵/0.1) = √(1.8 × 10⁻⁴) = 0.0424 = 4.24%

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Q.19 Hard NEET Chemistry Physical Chemistry

The standard electrode potentials are: Cu²⁺ + 2e⁻ → Cu, E° = 0.34 V and Ag⁺ + e⁻ → Ag, E° = 0.80 V. Which is the strongest oxidizing agent?

A Cu²⁺

B Cu

C Ag⁺

D Ag

Correct Answer: C. Ag⁺

EXPLANATION

Higher the reduction potential, stronger the oxidizing agent. Ag⁺ (E° = 0.80 V) > Cu²⁺ (E° = 0.34 V). Ag⁺ is strongest oxidizer.

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Q.20 Hard NEET Chemistry Physical Chemistry

For the reaction: 2A + B ⇌ C, Kc = 0.5 at 298 K. If initial concentrations are [A] = 1 M, [B] = 1 M, [C] = 0, what is the equilibrium concentration of C?

A 0.414 M

B 0.268 M

C 0.536 M

D 0.707 M

Correct Answer: A. 0.414 M

EXPLANATION

ICE table: At equilibrium, [A] = 1-2x, [B] = 1-x, [C] = x. Kc = x/[(1-2x)²(1-x)] = 0.5. Solving: x ≈ 0.414 M

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