NEET Chemistry - MCQ Practice Questions

Boiling points of hydrides depend on intermolecular forces, which vary based on molecular mass and hydrogen bonding strength.

Step 1: Identify Group 16 Hydrides and Their Boiling Points

Group 16 elements (chalcogens) form hydrides with the general formula H₂X. Let's list their boiling points:

Step 2: Analyze Intermolecular Forces

H₂O has exceptional boiling point due to strong hydrogen bonding between oxygen (highly electronegative) and hydrogen. However, S, Se, and Te are less electronegative, so H₂S, H₂Se, and H₂Te exhibit only weak dipole-dipole interactions and London dispersion forces:

Among H₂S, H₂Se, and H₂Te, molecular mass increases down the group, strengthening London dispersion forces. H₂S has the smallest molecular mass (34 g/mol) among these three, resulting in the weakest intermolecular forces.

The correct answer is (B) H₂S with a boiling point of -60°C, the lowest among the group.

At 25°C (298 K), (2.303RT/F) = (2.303 × 8.314 × 298)/96485 ≈ 0.0592 V. This is commonly used in half-cell potential calculations.

For a first-order reaction, the relationship between time, concentration, and rate constant follows a logarithmic decay pattern that connects to the half-life.

Step 1: Apply the First-Order Rate Law

For a first-order reaction, we use the integrated rate equation that relates remaining concentration to time.

Since the reaction is 75% complete, 25% of the reactant remains, so $\frac{[A{]}_t}{[A{]}_0}=0.25$ or $\frac{[A{]}_0}{[A{]}_t}=4$

Step 2: Calculate Half-Life Using the Half-Life Formula

The half-life for a first-order reaction is independent of initial concentration and is given by:

The half-life of the reaction is 22.5 minutes.

The answer is (B) 22.5 minutes.

At equilibrium, the chemical potential of a substance is the same in all phases present. This is the condition for phase equilibrium.

Initial: PA = 2, PB = 1. Change: -1.5 for A, -1.5 for B, +1.5 for C and D. Equilibrium: PA = 0.5, PB = -0.5 (invalid). Using Kp: 4 = (PC × PD)/(0.5 × PB). Since stoichiometry is 1:1:1:1, PC = PD = 1.5 atm.