$\mathrm{He}, \mathrm{Ar}$

$\mathrm{Ar}, \mathrm{He}$

$\mathrm{He}, \mathrm{Kr}$

$\mathrm{Ar}, \mathrm{Kr}$

$\mathrm{HPO}_3, \mathrm{PH}_3$

$\mathrm{H}_3 \mathrm{PO}_2, \mathrm{H}_2 \mathrm{O}$

$\mathrm{H}_3 \mathrm{PO}_4, \mathrm{PH}_3$

$\mathrm{H}_4 \mathrm{P}_2 \mathrm{O}_6, \mathrm{H}_3 \mathrm{PO}_2$

$\mathrm{B}_2 \mathrm{H}_6, \mathrm{AlH}_3$

$\mathrm{NaH}, \mathrm{MgH}_2$

$\mathrm{HCl}, \mathrm{H}_2 \mathrm{~S}$

$\mathrm{CH}_4, \mathrm{SiH}_4$

All the trihalides exist except $\mathrm{TII}_3$.

Trihalides on hydrolysis form tetrahedral species.

Diborane is an example of electron precise hydride.

Hydrolysis of diborane gives boric acid.