Question

what is covalent hydrides ?

Answer 1

Covalent hydrides: They include the hydrocarbons and many other compounds which covalently bond to hydrogen atoms. This category includes hydrides that exist as discrete molecules, polymers or oligomers, and hydrogen that has been chem-adsorbed to a surface.
Complex metal hydrides are commonly used in synthetic procedures. Sodium borohydride (NaBH₄) and lithium aluminium hydride (soluble in solvents) are widely used in organic synthesis.