Question

Why thermal stability decreases from HF to hi

Answer 1

thermal stability decreases from hf to hi because hydrogen and fluorine have comparable size because of which they are more stable and hold electron pairs easily whereas while moving down the group size of central atom increases and hence bond between central atom and hydrogen becomes less stable....therefore thermal stability decreases .............

Answer 2

Thermal stability depends on bond strength and bond dissociation enthalphy. While comparing F and I
Fluorine has High electronegativity and form strong bond with hydrides, therefore bond dissociation enthalphy is High implies thermal stability is High
Therefore HF has High thermal stability and it decreases down the halogen group.

Hope my answer helps you.