A ' p '-block element $(\mathrm{E})$ and hydrogen form a binary cation $\left(\mathrm{EH}_{\mathrm{x}}\right)^{+}$, while $\mathrm{EH}_{3}$ on treatment with $\mathrm{K}_{2} \mathrm{HgI}_{4}$ in alkaline medium gives a precipitate of basic mercury(II)amido-iodine. Given below are first ionisation enthalpy values $\left(\mathrm{kJ} \mathrm{mol}^{-1}\right)$ for first element each from group 13, 14, 15 and 16. Identify the correct first ionisation enthalpy value for element E.

The p-block element E forms a binary cation $(EH_x)^+$ with hydrogen and produces a basic mercury(II) amido-iodide precipitate with $K_2HgI_4$ in alkaline medium.
This behavior is characteristic of ammonia (NH₃), which forms the ammonium ion $(NH_4)^+$ and reacts with Nessler's reagent ($K_2HgI_4$) to form a characteristic brown/yellow precipitate.
Therefore, E is Nitrogen (N), a Group 15 p-block element with electronic configuration $1s^2 2s^2 2p^3$.
Nitrogen has a notably high first ionization enthalpy compared to other group 15 elements due to:
Small atomic radius
High effective nuclear charge
Stable half-filled p³ subshell configuration
The first ionization enthalpy of nitrogen is 1402 kJ/mol.