How many of the following are electron deficient Hydrides

${\mathrm{CH}}_4,{\mathrm{SiH}}_4,{\mathrm{AlH}}_3,{\mathrm{GaH}}_3,{\mathrm{C}}_2{\mathrm{H}}_6,{\mathrm{NH}}_3,{\mathrm{H}}_2\mathrm{O},{\mathrm{B}}_2{\mathrm{H}}_6$

IIIA – group hydrides are electron deficient hydride 

The molecular hydrides which have less number of valency electrons in central atom to form chemical bond are called electron deficient.

${\mathrm{AlH}}_3,{\mathrm{GaH}}_3,{\mathrm{B}}_2{\mathrm{H}}_6$