Concept: This question tests the understanding of various chemical properties and their trends, including bond angle, dipole moment, bond order, and paramagnetic nature.

Why (A) is correct:

Bond Angle: The bond angle in hydrides of Group 15 elements decreases down the group. This is due to the decrease in electronegativity of the central atom (N > P > As > Sb). As electronegativity decreases, the bond pair electrons are less attracted towards the central atom and more towards the hydrogen atoms. This reduces the repulsion between bond pairs and increases the repulsion between lone pair and bond pairs, leading to a decrease in bond angle. Also, as the size of the central atom increases, the bond length increases, and the bond pairs are further away, reducing their mutual repulsion. The bond angles are approximately: NH₃ (107.8°), PH₃ (93.5°), AsH₃ (91.8°), SbH₃ (91.3°). Thus, the order NH₃ > PH₃ > AsH₃ > SbH₃ is correct.

Option Analysis:

• B) CH₃Cl > CH₂Cl₂ > CHCl₃ > CCl₄ (Dipole moment): The correct order of dipole moment is CH₃Cl > CHCl₃ > CH₂Cl₂ > CCl₄. CCl₄ has zero dipole moment due to its symmetrical tetrahedral structure. The dipole moments are approximately: CH₃Cl (1.87 D), CH₂Cl₂ (1.60 D), CHCl₃ (1.03 D), CCl₄ (0 D).
• C) O₂ > N₂ > C₂ > B₂ (Bond order): The correct order of bond order is N₂ (3) > O₂ (2) > C₂ (2) > B₂ (1). (Note: C₂ has a bond order of 2, and B₂ has a bond order of 1).
• D) O₂ > O₂⁺ = O₂⁻ > O₂²⁻ (Paramagnetic nature): Paramagnetic nature depends on the number of unpaired electrons. The number of unpaired electrons are: O₂⁺ (1), O₂ (2), O₂⁻ (1), O₂²⁻ (0). Therefore, the correct order of paramagnetic nature (number of unpaired electrons) is O₂ (2) > O₂⁺ (1) = O₂⁻ (1) > O₂²⁻ (0). The given order is incorrect.

Correct Answer: (A)