In the ring test of $NO_{3}^{-}$ ion,$Fe^{2+}$ ion reduces nitrate ion to nitric oxide,which combines with $Fe^{2+}_{(aq)}$ ion to form a brown complex. Write the reactions involved in the formation of the brown ring.

$A$ metalloid is

Given below are two statements:
Statement-$I$: Element '$X$' and '$Y$' are the most and least electronegative elements, respectively, among $N, As, Sb$ and $P$. The nature of the oxides $X_{2}O_{3}$ and $Y_{2}O_{3}$ is acidic and amphoteric, respectively.
Statement-$II$: $BCl_{3}$ is covalent in nature and gets hydrolysed in water. It produces $[B(OH)_{4}]^{-}$ and $HCl$ in aqueous medium.

Which element from group $15$ ($V$ group) forms the most basic compound with hydrogen?

Regarding the hydrides of group $15$ elements $EH_{3}$ $(E = N, P, As, Sb, Bi)$, select the correct statement from the following:
$A$. The stability of hydrides decreases down the group.
$B$. The basicity of hydrides decreases down the group.
$C$. The reducing character increases down the group.
$D$. The boiling point increases down the group.
Choose the correct answer from the options given below:

Pure concentrated $HNO_3$ makes iron passive as the surface is covered with a protective layer of: