What are hydrides? Give their types and explain.

(N/A) Dihydrogen,under certain reaction conditions,combines with almost all elements,except noble gases,to form binary compounds,called hydrides.
If $E$ is the symbol of an element,then the hydride can be expressed as $EH_{x}$ (e.g.,$MgH_{2}$) or $E_{m}H_{n}$ (e.g.,$B_{2}H_{6}$).
The hydrides are classified into three categories:
$(i)$ Ionic or saline or salt-like hydrides: These are stoichiometric compounds of dihydrogen formed with most of the $s$-block elements which are highly electropositive in character.
$(ii)$ Covalent or molecular hydrides: These are compounds of dihydrogen formed with most of the $p$-block elements.
$(iii)$ Metallic or non-stoichiometric hydrides: These are formed by many $d$-block and $f$-block elements. These hydrides are often non-stoichiometric,being deficient in hydrogen.