The correct order of first ionization enthalpy values of the following elements is: (A) O (B) N (C) Be (D) F (E) B Choose the correct answer from the options given below:

Chemistry · Periodicity of Elements and Periodic Properties

JEE Main 2024 — 4 April, Shift 1 — Question 73

The correct order of first ionization enthalpy values of the following elements is:

(A) $\mathrm{O}$ (B) $\mathrm{N}$ (C) $\mathrm{Be}$ (D) $\mathrm{F}$ (E) $\mathrm{B}$

Choose the correct answer from the options given below:

All elements belong to period 2. First ionization enthalpy generally increases across a period due to increase in effective nuclear charge.

Important exceptions, we have

$\mathrm{B < Be}$ because in B the electron is removed from a $2p$ orbital (higher energy), whereas in Be it is removed from $2s$ .

$\mathrm{O < N}$ because O has paired electrons in $2p$ orbital causing extra repulsion, while N has stable half-filled $2p^3$ configuration.

Now arranging in increasing order is $\mathrm{B < Be < O < N < F}$ .

Thus, the corresponding letters are E < C < A < B < D.

Hence, the correct option is B.

Answer key and solution verified before publishing.

Start with this question, then two more from the same chapter — with a tutor that explains every step. Free.

Exam: JEE Main 2024
Paper: 4 April, Shift 1
Subject: Chemistry
Chapter: Periodicity of Elements and Periodic Properties
Topic: Periodicity in Chemical Properties (Ionization Energy, Electron Affinity, Electronegativity)