JEE Main 2026 — Jan 22, Shift 1 — Chemistry solution

JEE Main2026Jan 22, Shift 1Chemistry

A ‘p’-block element (E) and hydrogen form a binary cation $(E H_{x})^{+}$ , while $E H_{3}$ on treatment with $K_{2} H g I_{4}$ in alkaline medium gives a precipitate of basic mercury(II) amido-iodine. Given below are first ionisation enthalpy values (kJ mol $^{- 1}$ ) for first element each from group 13, 14, 15 and 16. Identify the correct first ionisation enthalpy value for element E.

A
1312
B
1086
C
1402
D
801

Solution

The clues identify E as nitrogen: $(E H_{x})^{+} = N H_{4}^{+}$ , and $N H_{3} + K_{2} H g I_{4} + K O H$ is Nessler’s test, giving a brown precipitate of $H g O \cdot H g (N H_{2}) I$ (iodide of Millon’s base).

Among the first elements of groups 13–16 (B, C, N, O), nitrogen has the highest first ionisation enthalpy because of the extra stability of its half-filled $2 p^{3}$ configuration.

Standard values: B = 801, C = 1086, O = 1312, N = 1402 kJ mol $^{- 1}$ . So $I E_{1} (N) = 1402$ .

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