Explanation

(d)
$Ba\ \left( N_{3} \right)_{2}$⟶Ba(s)+3N_{2}(g)
Azide salt of barium can be obtained in purest form as well as the decomposition product contain solid Ba as by product alongwith gaseous nitrogen hence to additional step of separation is required.
Other reaction are
NH_{4} NO_{3}$\overset{Heat}{\rightarrow}$ N_{2}O+2H_{2}O
2 NH_{3} + 3CuO $\overset{Heat}{\rightarrow}$3Cu+3H_{2}O+N_{2}
(NH_{4})_{2}Cr_{2}O_{7}$\overset{Heat}{\rightarrow}$ Cr_{2}O_{3} +4H_{2}O +N_{2}