For elements $\mathrm{B}, \mathrm{C}, \mathrm{N}, \mathrm{Li}, \mathrm{Be}, \mathrm{O}$ and F the correct order of first ionization enthalpy is

(C) $\mathrm{Li}<\mathrm{B}<\mathrm{Be}<\mathrm{C}<\mathrm{O}<\mathrm{N}<\mathrm{F}$

(A) $\mathrm{Li}<\mathrm{Be}<\mathrm{B}<\mathrm{C}<\mathrm{N}<\mathrm{O}<\mathrm{F}$

(B) B $>$ Li $>$ Be $>$ C $>$ N $>$ O $>$ F

(D) $\mathrm{Li}<\mathrm{Be}<\mathrm{B}<\mathrm{C}<\mathrm{O}<\mathrm{N}<\mathrm{F}$

JEE Main · 2023 · 11 Apr 2023 · Shift 1 · Classification of Elements and Periodicity

For elements

B, C, N, Li, Be, O

and F the correct order of first ionization enthalpy is

(A) $Li < Be < B < C < N < O < F$
(B)B $>$ Li $>$ Be $>$ C $>$ N $>$ O $>$ F
(C) $Li < B < Be < C < O < N < F$ ✓ Correct
(D) $Li < Be < B < C < O < N < F$

Answer: (C)

Solution

First ionization enthalpy generally increases across a period due to increasing nuclear charge. However, there are two key exceptions: (1) B has lower IE than Be because removing an electron from B's 2p orbital is easier than from Be's filled 2s orbital. (2) O has lower IE than N because N has a half-filled, stable 2p³ configuration, while O's 2p⁴ has electron-electron repulsion in one of the orbitals. The correct order is: Li (520) < B (801) < Be (899) < C (1086) < O (1314) < N (1402) < F (1681) kJ/mol.

JEE Main · 2023 · 11 Apr 2023 · Shift 1 · Single correct option

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JEE Main · 2023 · 11 Apr 2023 · Shift 1 · Classification of Elements and Periodicity

Solution

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