In which oxidation state,group $15$ elements act as Lewis base?

Identify the element for which $+1$ oxidation state is more stable than $+3$ oxidation state.

$A$ tetra-atomic molecule $(A)$ on reaction with excess oxygen produces substance $(B)$. $(B)$ is a dehydrating agent. The substances $(A)$ and $(B)$ respectively will be:

At high temperatures,nitrogen directly combines with

Which of the compounds among $N_2O, NO, N_2O_3, NO_2, N_2O_4, N_2O_5$ are diamagnetic?

Calcium phosphide reacts with water to form $Ca(OH)_2$ and $X$. When $X$ is passed into $CuSO_4$ solution,$Y$ and $H_2SO_4$ are formed. What is $Y$?