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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 41–50 of 904
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Q.41 Medium NEET Chemistry Physical Chemistry
The standard cell potential for a cell is E° = 1.10 V. Calculate ΔG° (F = 96500 C/mol, n = 2):
A -212.3 kJ/mol
B +212.3 kJ/mol
C -106.15 kJ/mol
D +106.15 kJ/mol
Correct Answer:  A. -212.3 kJ/mol
EXPLANATION

ΔG° = -nFE° = -2 × 96500 × 1.10 = -212,300 J/mol = -212.3 kJ/mol.

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Q.42 Medium NEET Chemistry Physical Chemistry
For a reversible adiabatic process of an ideal gas, which statement is correct?
A ΔS = 0 (entropy is constant)
B ΔU = 0
C q = 0 and ΔS > 0
D ΔH = 0
Correct Answer:  A. ΔS = 0 (entropy is constant)
EXPLANATION

For a reversible adiabatic process, q = 0 and ΔS = 0 because there is no heat exchange and the process is reversible, making it isentropic.

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Q.43 Easy NEET Chemistry Physical Chemistry
A solution has pH = 4. What is the concentration of H⁺ ions?
A 1 × 10⁻⁴ M
B 1 × 10⁻³ M
C 4 × 10⁻¹ M
D 1 × 10⁻⁴⁰ M
Correct Answer:  A. 1 × 10⁻⁴ M
EXPLANATION

pH = -log[H⁺], so [H⁺] = 10⁻ᵖᴴ = 10⁻⁴ = 1 × 10⁻⁴ M.

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Q.44 Medium NEET Chemistry Physical Chemistry
In electrochemistry, what does the cell potential (E°cell) indicate?
A The voltage of the battery
B The maximum work that can be obtained from the cell
C The rate of the reaction
D The concentration of electrolyte
Correct Answer:  B. The maximum work that can be obtained from the cell
EXPLANATION

E°cell is directly related to the maximum electrical work (w_max = -nFE°cell) that can be obtained from a galvanic cell.

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Q.45 Medium NEET Chemistry Physical Chemistry
The hydration enthalpy of an ion depends on which of the following factors?
A Charge and size of the ion only
B Only the temperature
C Only the solvent used
D Pressure and temperature
Correct Answer:  A. Charge and size of the ion only
EXPLANATION

Hydration enthalpy depends on the charge density of the ion (charge/size ratio). Higher charge and smaller size lead to greater hydration enthalpy.

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Q.46 Medium NEET Chemistry Physical Chemistry
For the equilibrium PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), Kc = 1.8 at 298 K. If initial concentration of PCl₅ is 1 M, find [PCl₃] at equilibrium when dissociation is 30%.
A 0.3 M
B 0.7 M
C 0.6 M
D 0.9 M
Correct Answer:  A. 0.3 M
EXPLANATION

If 30% of PCl₅ dissociates, [PCl₃] = 1 × 0.30 = 0.3 M and [Cl₂] = 0.3 M.

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Q.47 Easy NEET Chemistry Physical Chemistry
Which of the following is true for an endothermic reaction?
A ΔH is negative
B ΔH is positive
C Heat is released to surroundings
D Temperature of surroundings increases
Correct Answer:  B. ΔH is positive
EXPLANATION

In endothermic reactions, ΔH is positive because heat is absorbed from surroundings. The system absorbs energy.

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Q.48 Easy NEET Chemistry Physical Chemistry
A first-order reaction has a rate constant k = 0.693 s⁻¹. Calculate the half-life of this reaction.
A 1.0 s
B 0.5 s
C 2.0 s
D 1.5 s
Correct Answer:  A. 1.0 s
EXPLANATION

For first-order reactions, t₁/₂ = 0.693/k = 0.693/0.693 = 1.0 s.

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Q.49 Easy NEET Chemistry Physical Chemistry
What is the cell potential (E°cell) for a galvanic cell with E°cathode = +0.80 V and E°anode = -0.40 V?
A +1.20 V
B +0.40 V
C -0.40 V
D +0.80 V
Correct Answer:  A. +1.20 V
EXPLANATION

E°cell = E°cathode - E°anode = 0.80 - (-0.40) = 1.20 V. A positive E°cell indicates a spontaneous galvanic cell.

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Q.50 Medium NEET Chemistry Physical Chemistry
The rate of reaction doubles when temperature increases from 300 K to 310 K. Calculate the activation energy (Ea) using Arrhenius equation.
A 52.8 kJ/mol
B 52.8 J/mol
C 105.6 kJ/mol
D 26.4 kJ/mol
Correct Answer:  A. 52.8 kJ/mol
EXPLANATION

Using ln(k₂/k₁) = (Ea/R)(T₂-T₁)/(T₁T₂), ln(2) = (Ea/8.314)(10)/(93000). Solving: Ea ≈ 52.8 kJ/mol.

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