a. Element with atomic number, `Z=15`,i.e., phosphourous `(P)` is a non-metal and hence the hydride formed is covalent, i.e. `PH_(3)`
b. Element with `Z=19` is potassium `(K)` an alkali metal and hence the hydride formed is ionic , i.e. `KH`.
c. Element with `Z=23` , is a transition metal, i.e. vanadium `(V)` and hence the hydride formed is metallic or interstitial .`(VH_(0.56))`
d. Element with `Z=44` is a transition metal, i.e. ruthenicum `(Ru)` and does not form any hydride (hydride gap). Behaviour towards water:Only ionic hydrides react with water. Forming corresponding metal hydroxide and evolve `H_(2)` gas.