JEE Chemistry — MCQ Practice Questions & Answers

Question 1

Which of the following has the highest lattice energy?

Accepted Answer

Correct answer: B. MgO — According to Coulomb's law, lattice energy is proportional to the product of the ionic charges divided by the distance between ions: U \propto \frac{|q_+|\,|q_-|}{r} **Step 1: Consider the ionic charges.** 	ext{MgO} consists of 	ext{Mg}^{2+} and 	ext{O}^{2-} ions, giving a charge product of |{+2}|	imes|{-2}| = 4 , which is larger than that of singly charged ion pairs. **Step 2: Consider the ionic radii.** The ions 	ext{Mg}^{2+} and 	ext{O}^{2-} have relatively small ionic radii, so the interionic distance r is small. A smaller r leads to a larger lattice energy. **Step 3: Combine both factors.** Since 	ext{MgO} has both a high charge product and a small interionic distance, U_{	ext{MgO}} \propto \frac{|{+2}|	imes|{-2}|}{r_{	ext{small}}} this results in a stronger electrostatic attraction and therefore the highest lattice energy among the given options. **Conclusion:** \boxed{	ext{MgO has the highest lattice energy.}}

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A. NaCl

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C. KCl

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D. CaO

Question 2

The vapour pressure of a liquid depends on:

Accepted Answer

Correct answer: B. Temperature and nature of the liquid — Vapour pressure depends on the following factors: **Step 1: Effect of Temperature** As temperature increases, more molecules have sufficient kinetic energy to escape the liquid phase, so vapour pressure increases. In general, 	ext{Vapour pressure} \uparrow \quad 	ext{as} \quad T \uparrow **Step 2: Effect of Intermolecular Forces** The nature of intermolecular forces in the liquid determines how easily molecules can escape into the vapour phase. Liquids with weaker intermolecular forces have higher vapour pressures, and those with stronger intermolecular forces have lower vapour pressures: 	ext{Stronger intermolecular forces} \implies 	ext{Lower vapour pressure} **Step 3: Factors That Do NOT Affect Vapour Pressure** Surface area and volume of the liquid do **not** affect the vapour pressure: 	ext{Vapour pressure} 
e f(	ext{surface area}) 	ext{Vapour pressure} 
e f(	ext{volume}) **Conclusion** Vapour pressure depends only on: \boxed{	ext{Temperature} \quad 	ext{and} \quad 	ext{Nature of intermolecular forces}}

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A. Surface area only

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C. Volume of the liquid

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D. Atmospheric pressure

Question 3

Which colligative property is independent of the nature of solute?

Accepted Answer

Correct answer: B. Boiling point elevation — Boiling point elevation depends only on the number of solute particles (expressed as molality m ), not on their chemical nature. The relationship is given by \Delta T_b = K_b \cdot m where K_b is the ebullioscopic (boiling point elevation) constant of the solvent and m is the molality of the solution. Since \Delta T_b depends solely on m (the number of solute particles per kilogram of solvent) and K_b (a property of the solvent alone), it is completely independent of the chemical nature of the solute. \boxed{\Delta T_b = K_b \cdot m}

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A. Optical activity

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C. Refractive index

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D. Specific rotation

Question 4

For a spontaneous process at constant T and P, the condition is:

Accepted Answer

Correct answer: C. ΔG < 0 — At constant temperature and pressure, the criterion for spontaneity is \Delta G < 0, where the Gibbs free energy change is defined as \Delta G = \Delta H - T\,\Delta S. A process is spontaneous when the enthalpy and entropy contributions combine such that \Delta H - T\,\Delta S < 0 , meaning the system lowers its Gibbs free energy. The final condition is therefore \boxed{\Delta G < 0.}

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A. ΔH < 0

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B. ΔS > 0

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D. ΔU < 0

Question 5

Which of the following is an extensive property?

Accepted Answer

Correct answer: C. Entropy — **Step 1: Identify the property type.** A property is **extensive** if it depends on the amount (or size) of the system, and **intensive** if it does not. **Step 2: Classify each property.** \begin{aligned} 	ext{Entropy } (S) &: 	ext{extensive} \quad (	ext{depends on amount of substance}) \ 	ext{Refractive index } (n) &: 	ext{intensive} \ 	ext{Surface tension } (\gamma) &: 	ext{intensive} \ 	ext{Density } (ho) &: 	ext{intensive} \end{aligned} **Step 3: Conclusion.** Entropy S scales with the size of the system — doubling the amount of substance doubles the entropy. The remaining properties (refractive index, surface tension, and density) are independent of the amount of substance, making them intensive. \boxed{S = 	ext{Entropy is an extensive property.}}

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A. Refractive index

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B. Surface tension

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D. Density

Question 6

The osmotic pressure of a solution is given by:

Accepted Answer

Correct answer: C. π = CRT — **Osmotic Pressure** The osmotic pressure of a solution is given by: \pi = CRT where: - \pi is the osmotic pressure, - C is the molar concentration of the solute, - R is the universal gas constant, - T is the absolute temperature. Osmotic pressure is a colligative property, meaning it depends on the **number of solute particles** present in the solution, not on their chemical identity. \boxed{\pi = CRT}

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A. π = nRT/V

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B. π = MRT

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D. π = dRT

Question 7

The first ionization energy of sodium is lower than that of hydrogen because:

Accepted Answer

Correct answer: D. Both A and B — Both the larger atomic radius and the greater shielding effect in sodium make the valence electron easier to remove compared to hydrogen's single electron. **Step 1: Effective Nuclear Charge** The effective nuclear charge Z_{	ext{eff}} experienced by the valence electron is approximated by Slater's rules: Z_{	ext{eff}} = Z - \sigma where Z is the atomic number and \sigma is the shielding constant. - For hydrogen ( Z = 1 ): \sigma = 0 , so Z_{	ext{eff}} = 1 . - For sodium ( Z = 11 ): the inner electrons (1s², 2s², 2p⁶) provide significant shielding, giving \sigma \approx 8.8 , so Z_{	ext{eff}} \approx 2.2 . However, despite sodium having a higher Z_{	ext{eff}} than hydrogen's Z_{	ext{eff}} = 1 in absolute terms, the valence electron in sodium resides in the n = 3 shell, which is much farther from the nucleus. **Step 2: Distance and Ionization Energy** The ionization energy scales approximately as: IE \propto \frac{Z_{	ext{eff}}}{r} Since the atomic radius of sodium ( r_{	ext{Na}} \approx 186\ 	ext{pm} ) is far larger than that of hydrogen ( r

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A. Sodium has larger atomic radius

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B. Sodium has better shielding effect

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C. Sodium nucleus has lower charge

Question 8

At 25°C, the solubility product (Ksp) of AgCl is 1.8 × 10⁻¹⁰. What is the molar solubility of AgCl in pure water?

Accepted Answer

Correct answer: A. 1.34 × 10⁻⁵ M — **Step 1: Write the dissolution equilibrium** For the dissolution of AgCl in pure water: 	ext{AgCl}(s) ightleftharpoons 	ext{Ag}^+(aq) + 	ext{Cl}^-(aq) **Step 2: Set up the expression for K_{sp} ** Let s be the molar solubility of AgCl. Then [	ext{Ag}^+] = s and [	ext{Cl}^-] = s , so: K_{sp} = [	ext{Ag}^+][	ext{Cl}^-] = s 	imes s = s^2 **Step 3: Solve for s ** \begin{aligned} s^2 &= 1.8 	imes 10^{-10} \ s &= \sqrt{1.8 	imes 10^{-10}} \ s &= 1.34 	imes 10^{-5} \ 	ext{M} \end{aligned} **Result:** \boxed{s = 1.34 	imes 10^{-5} \ 	ext{M}}

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B. 4.24 × 10⁻⁶ M

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C. 2.68 × 10⁻⁵ M

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D. 9 × 10⁻¹¹ M

JEE Chemistry - MCQ Practice Questions