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JEE Main MCQ questions — Mathematics, Physics, Chemistry for engineering entrance.

487 Q 3 Subjects 12th (PCM)
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Q.481 Easy JEE Chemistry Physical Chemistry
Which of the following is an extensive property?
A Refractive index
B Surface tension
C Entropy
D Density
Correct Answer:  C. Entropy
EXPLANATION

Entropy is an extensive property (depends on amount of substance). Refractive index, surface tension, and density are intensive properties.

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Q.482 Medium JEE Chemistry Physical Chemistry
The rate constant of a reaction at 25°C is k₁ and at 75°C is k₂. If Ea = 60 kJ/mol, what is k₂/k₁? (R = 8.314 J/mol·K)
A 10.3
B 25.8
C 103
D 258
Correct Answer:  C. 103
EXPLANATION

Using Arrhenius equation: ln(k₂/k₁) = (Ea/R)(1/T₁ - 1/T₂) = (60000/8.314)(1/298 - 1/348) ≈ 4.63, so k₂/k₁ ≈ 103.

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Q.483 Easy JEE Chemistry Physical Chemistry
For a spontaneous process at constant T and P, the condition is:
A ΔH < 0
B ΔS > 0
C ΔG < 0
D ΔU < 0
Correct Answer:  C. ΔG < 0
EXPLANATION

At constant temperature and pressure, ΔG < 0 is the criterion for spontaneity, where ΔG = ΔH - TΔS.

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Q.484 Easy JEE Chemistry Physical Chemistry
Which colligative property is independent of the nature of solute?
A Optical activity
B Boiling point elevation
C Refractive index
D Specific rotation
Correct Answer:  B. Boiling point elevation
EXPLANATION

Boiling point elevation depends only on the number of solute particles (molality), not on their chemical nature.

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Q.485 Medium JEE Chemistry Physical Chemistry
At critical point, the compressibility factor Z equals:
A 1
B 0.5
C 0.27
D 2
Correct Answer:  C. 0.27
EXPLANATION

At the critical point, Z = PcVc/RTc = 0.27 for most real gases (theoretical value for van der Waals gas).

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Q.486 Easy JEE Chemistry Physical Chemistry
The vapour pressure of a liquid depends on:
A Surface area only
B Temperature and nature of the liquid
C Volume of the liquid
D Atmospheric pressure
Correct Answer:  B. Temperature and nature of the liquid
EXPLANATION

Vapour pressure depends on temperature (increases with temperature) and the nature of intermolecular forces in the liquid, not on surface area or volume.

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Q.487 Easy JEE Chemistry Physical Chemistry
Which of the following has the highest lattice energy?
A NaCl
B MgO
C KCl
D CaO
Correct Answer:  B. MgO
EXPLANATION

MgO has the highest lattice energy due to smaller ionic radii of Mg²⁺ and O²⁻ ions, leading to stronger electrostatic attractions.

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