Thallium shows different oxidation states because

Identify the incorrect statements about group $15$ elements :
$A$. Dinitrogen is a diatomic gas which acts like an inert gas at room temperature.
$B$. The common oxidation states of these elements are $-3, +3$ and $+5$.
$C$. Nitrogen has unique ability to form $p\pi-p\pi$ multiple bonds.
$D$. The stability of $+5$ oxidation states increases down the group.
$E$. Nitrogen shows a maximum covalency of $6$.
Choose the correct answer from the options given below.

Nitrogen shows different oxidation states in the range of:

Small quantities of $NO$ and $HNO_3$ are formed as impurities when $N_2$ is prepared from $NH_4Cl_{(aq)}$ and $NaNO_{2(aq)}$. These impurities can be removed by passing the $N_2$ gas through which of the following?

Which one of the following is used to remove moisture from ammonia gas?

Explain the molecular structure and properties of phosphorus pentachloride $(PCl_5)$.