Bond dissociation energy of E-H bond of the H2E hydrides of group 16 elements follows order: (A) O (B) S (C) Se (D) Te

🧠 As you go down Group 16, the central atom gets bigger, the E–H bond gets longer, and the bond gets weaker Bond dissociation energy (BDE) follows bond length: shorter bonds need more energy to break. The smallest atom in Group 16 is oxygen, so the O–H bond is the shortest and strongest. Going O → S → Se → Te the atom expands, the bond stretches, and BDE drops steadily.

🗺️ Map letters and rank A = O, B = S, C = Se, D = Te. Approximate H–E bond enthalpies (kJ/mol): $\ce{H-O}$: $\approx 463$. $\ce{H-S}$: $\approx 347$. $\ce{H-Se}$: $\approx 276$. $\ce{H-Te}$: $\approx 238$.

Order: O > S > Se > Te → A > B > C > D.

⚠️ The trap The order looks like a smooth decrease — but the SIZE of the drops is not even. The drop from O–H to S–H is huge (~115 kJ/mol) compared to S–H to Se–H (~70). Don't try to guess "the drop is constant"; just remember the chain: bigger atom = longer bond = weaker bond. The order is monotonic, the magnitudes are not.

$\boxed{\text{Answer: (a)}}$