Elements of group- 15, 16, and 17 form compounds with hydrogen with general formula \(MH_3\), \(H_2M\), and \(HX\) (called hydrogen halides). The stability of these hydrides, along with \(M-H\) bond strength and basic nature decreases down the group. Boiling point of these hydrides mainly depends on the strength of their intermolecular forces.

The bond angle \(HMH\) among hydrides of group 16 decreases down the group because:

Electronegativity of the central atom decreases down the group

The correct answer is option 1. Electronegativity of the central atom decreases down the group.

Let us look at the reason for this trend:

1. Decreasing Electronegativity: As you move down group 16 (O, S, Se, Te), the electronegativity of the central atom decreases. This means the central atom attracts less electron density towards itself, weakening the bonding electron pairs (M-H) and allowing them to spend more time closer to the hydrogen atoms.
2. Increased H-H Repulsion: Weaker bonding electron pairs lead to less effective shielding of the hydrogen atoms from each other. This weaker shielding increases the repulsive interaction between the hydrogen atoms (H-H repulsion), causing the HMH bond angle to decrease.

While lone pair-bond pair repulsion can also contribute slightly to the trend, it is not the main reason. Larger lone pairs in bigger central atoms might occupy more space and cause some repulsion with bond pairs, but their effect is much smaller compared to the dominant effect of decreasing electronegativity and increasing H-H repulsion.