Which element from following combines with hydrogen to form a compound with lowest thermal stability?
Which element from following combines with hydrogen to form a compound with lowest thermal stability?
F
Cl
I
Br
Solution
The bond dissociation enthalpy of $\mathrm{H}-\mathrm{X}$ bond decreases in the order: $\mathrm{HF} \gt \mathrm{HCl} \gt \mathrm{HBr} \gt \mathrm{HI}$. Therefore, thermal stability of hydrogen halides also decreases in the order:
$\mathrm{HF} \gt \mathrm{HCl} \gt \mathrm{HBr} \gt \mathrm{HI}$
$\therefore \quad$ Iodine combines with H to form a compound with lowest thermal stability.