What do you expect the nature of hydrides is,if formed by elements of atomic numbers $15, 19, 23$ and $44$ with dihydrogen? Compare their behaviour towards water.

(N/A) The elements of atomic numbers $15, 19, 23,$ and $44$ are phosphorus $(P)$,potassium $(K)$,vanadium $(V)$,and ruthenium $(Ru)$ respectively.
$1)$ Hydride of phosphorus $(PH_3)$:
Phosphorus forms a covalent molecular hydride. It is an electron-rich hydride due to the presence of a lone pair on the phosphorus atom.
$2)$ Hydride of potassium $(KH)$:
Potassium is a highly electropositive alkali metal. It forms an ionic (saline) hydride with dihydrogen. It is crystalline and non-volatile.
$3)$ Hydrides of vanadium $(V)$ and ruthenium $(Ru)$:
Both vanadium and ruthenium are $d$-block transition metals. They form metallic (interstitial) hydrides,which are often non-stoichiometric and conduct electricity.
$4)$ Behaviour towards water:
- Potassium hydride $(KH)$ reacts violently with water: $KH_{(s)} + H_2O_{(l)} \to KOH_{(aq)} + H_{2_{(g)}}$.
- Phosphine $(PH_3)$ is slightly soluble in water and acts as a very weak Lewis base.
- Metallic hydrides of vanadium and ruthenium are generally inert towards water.
Thus,the reactivity towards water follows the order: $KH > PH_3 > (V, Ru)H$.