Chemistry-I MCQs - 2025

• An exothermic reaction releases heat, so the enthalpy change (ΔH) is negative.

• ΔH > 0 (A) describes an endothermic reaction.

• ΔG (C, D) relates to Gibbs free energy, not heat exchange.

• Gas chromatography (GC) uses a gas mobile phase (e.g., He, N₂).

• The stationary phase is a liquid or solid.

• The Langmuir model assumes:

  1. Monolayer adsorption (not multilayer, eliminating A).

  2. Homogeneous surface sites with equal affinity.

  3. No interactions between adsorbed molecules.

• (C) is irrelevant (gas ideality is not an assumption).

• Calorimeters are calibrated using standard materials (e.g., benzoic acid) with known heats of combustion.

• (A) Bomb calorimeter is the device, not the method.

• Enzymes reduce activation energy (Eₐ) to accelerate reactions.

• They do not change equilibrium (C) or increase Eₐ (A).

• Lattice enthalpy (energy required to separate 1 mole of solid into gaseous ions) is always positive (endothermic).

• (B) and (D) confuse it with lattice energy (exothermic).

• Electrolytic cells require external energy (non-spontaneous).

• Anode is positive (B is wrong), and electrons flow from anode to cathode (A is reversed).

• Silicones contain Si-O backbones (inorganic) with organic side groups (e.g., –CH₃).

• They are not purely organic (A) or inorganic (B).

• Common ion effect (Le Chatelier’s principle) reduces solubility (e.g., adding NaCl to AgCl).

• High temperature (B) usually increases solubility.

• Potentiometry tracks potential difference (via electrodes) during titration.

• (A) refers to amperometry; (B) is volumetric analysis.

• Hess’s law states that ΔH depends only on initial and final states, not the reaction pathway.

• (A) and (C) contradict this.

• Zero-order reactions have a constant rate (rate = k), independent of reactant concentration.

• The rate depends on temperature (A) and may depend on pressure (B) for gases, but not [reactant].

• Fugacity ("effective pressure") corrects for non-ideal gas behavior.

• It is irrelevant to ideal gases (B) or equilibrium constants (C).

To determine which option does not have the ground-state electron configuration of 1s² 2s² 2p⁶, we need to look at the electron configurations of each species:

(A) Ne (Neon):

• Atomic number = 10

• Electron configuration = 1s² 2s² 2p⁶ ✅

(B) Na⁺ (Sodium ion):

• Atomic number of Na = 11

• Na: 1s² 2s² 2p⁶ 3s¹

• Na⁺ (after losing 1 electron) = 1s² 2s² 2p⁶ ✅

(C) Cl⁻ (Chloride ion):

• Atomic number of Cl = 17

• Cl: 1s² 2s² 2p⁶ 3s² 3p⁵

• Cl⁻ (after gaining 1 electron) = 1s² 2s² 2p⁶ 3s² 3p⁶ ❌
  (This is not 1s² 2s² 2p⁶ — it extends to the 3rd shell)

✅ Correct answer: (C) Cl⁻

This does not have the ground-state configuration 1s² 2s² 2p⁶.

• Multivariate calibration (e.g., PCR, PLS) uses multiple predictors (X-data) to model a response (Y-data).

• Options (B) and (C) are incorrect: Regression requires both X and Y data, and correlation alone is insufficient.

• Debye-Hückel theory estimates activity coefficients based on ionic strength (I).

• It does not directly calculate solubility (A) or Gibbs energy (C).