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(i) Electron deficient hydrides: Compounds in whichcentral atom has incomplete octet, are called electron deficient hydrides. Forexample, BeH2, BH3 are electron deficient hydrides.
(ii) Electron precise hydrides: Thosecompounds in which exact number of electrons are present in central atom or thecentral atom contains complete octet are called precise hydrides e.g., CH4,SiH4, GeH4 etc. are precise hydrides.
(iii) Electron rich hydrides: Thosecompounds in which central atom has one or more lone pair of excess electronsare called electron rich hydrides, e.g.,NH3, H2O.