Name the classes of hydrides to which H2O, B2 H6 and NaH belong.
H2O - Electron rich hydride.
H2O is an example of electron rich hydride. It contains excess number of electrons on the central atom called lone pairs. These are formed by group 15,16,17 elements like N, O, F, etc.
B2H6 - Electron deficient hydride.
B2H6 is an electron deficient hydride. These have an incomplete octet. They are formed generally by the group 13 elements like B, Al, etc.
NaH - Ionic hydride.
Hydrides formed with alkali and alkaline-earth metals. These compounds are ionic in nature.