Bond dissociation energy of "E-H" bond of the "H₂ E " hydrides of group 16 elements (given below), follows order.
A. O
B. S
C. Se
D. Te
Choose the correct from the options given below:

Solution

Chemistry ma’am · 3 steps

Down group 16 the atom gets bigger, overlaps less with tiny H, and the E–H bond gets weaker.

1. Size decides overlap. Going from O to Te, the atom grows larger and its bonding orbital becomes more diffuse. Overlap with the small 1s orbital of hydrogen gets poorer, so the E–H bond becomes longer and weaker.

   Hydride	E–H bond length	Bond dissociation enthalpy
   H₂O (A)	96 pm, shortest	463 kJ mol⁻¹, highest
   H₂S (B)	134 pm	347 kJ mol⁻¹
   H₂Se (C)	146 pm	276 kJ mol⁻¹
   H₂Te (D)	169 pm, longest	238 kJ mol⁻¹, lowest

2. Link to acidity. Because the bond weakens down the group, H⁺ is released more easily. That is why acidic strength rises from H₂O to H₂Te while thermal stability falls.
3. So. The E–H bond dissociation energy falls steadily down the group: O > S > Se > Te, that is, A > B > C > D, option (a).

The idea to keep. For hydrides down any group, a bigger central atom means poorer overlap with H, a longer and weaker E–H bond, higher acidity and lower thermal stability.

Answer from the NTA final answer key. Solution by PrepWiser.