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

Explanation

(i) Element with Z =15 is a non-metal (i.e. P) and hence forms covalent hydride (i.e. `PH_(3)`)
(ii) Element with Z=19 is an alkali metal (i.e. K) and hence forms saline or ionic hydride (i.e. `K^(+)H^(-)`)
(iii) Element with atomic number Z=23 is a transition metal (i.e. V) of group 3 and hence forms a metallic or insterstitial hydride (i.e. `VH_(0.56)`)
(iv) Element with Z=44 is a transition metal (i.e. Ru) of group 8 and hence does not form any hydride (hydride gap).
Behaviour towards water. Only ionic hydrides react with water evolving `H_(2)` gas. Thus,
`2KH(s) + 2H_(2)O(s) to 2KOH (aq) + 2H_(2)(q)`