Hello ….

Arrange the following in order of their increasing reducing property and please explain why so arranged ?.

NaH , MgH₂ and H₂O

ionic hydrides are strong reducing agent NAH can easily donate its electron . 
hence its most reducing , Mgh2 and H2o are covalent hydrides , h2o is less reducing than Mgh2 , since the bond dissociation energy of h2o is higher than mgh2 . 
hence , the increasing order 
H20
HOPE IT CLEARS