Which of the following elements forms oxides in all oxidation states from $+I$ to $+V$?

Which oxide is least acidic?

The reaction of $P_4$ with $X$ leads selectively to $P_4O_6$. The $X$ is

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

Pure $N_2$ gas is obtained from which of the following?

Which gas is used to provide an inert atmosphere?