Heating $(NH_4)_2Cr_2O_7$ liberates a gas. The same gas is obtained by:

Based on the compounds of group $15$ elements,the correct statement$(s)$ is (are):
$(A)$ $Bi_2O_5$ is more basic than $N_2O_5$
$(B)$ $NF_3$ is more covalent than $BiF_3$
$(C)$ $PH_3$ boils at a lower temperature than $NH_3$
$(D)$ The $N-N$ single bond is stronger than the $P-P$ single bond

Ionic radius (in $\mathring{A}$) of $As^{3+}$,$Sb^{3+}$ and $Bi^{3+}$ follow the order:

Identify the compound in which phosphorus exists in the oxidation state of $+1$.

The stability of $+1$ oxidation state increases in the sequence:

Find the element, which displays greater ability to form $p \pi-p \pi$ multiple bonds to itself and to other elements in the same block.