What is the covalence of nitrogen in `N_(2)O_(5)` ?

Explanation

(a) Covalency of nitrogen is `N_(2)O_(5)` is 4.
(b) As we move down the group, the size of element increases, the length of E-H bond increases and its strength decreases and can break more easily to evolve `H_(2)` gas which acts as reducing agent. The Bi-H bond is weaker than Sb-H. Hence, `BiH_(3)` is strong reducing agent than `SbH_(3)`.