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Chemistry · Periodicity of Elements and Periodic Properties

NEET (UG) 2024 — Question 78

Arrange the following elements in increasing order of first ionization enthalpy:

Li, Be, B, C, N

Choose the correct answer from the options given below:

  1. Option A:

    Li<Be<B<C<N\mathrm{Li}<\mathrm{Be}<\mathrm{B}<\mathrm{C}<\mathrm{N}

  2. Option B:

    Li<B<Be<C<N\mathrm{Li}<\mathrm{B}<\mathrm{Be}<\mathrm{C}<\mathrm{N}

    Correct
  3. Option C:

    Li<Be<C<B<N\mathrm{Li}<\mathrm{Be}<\mathrm{C}<\mathrm{B}<\mathrm{N}

  4. Option D:

    Li<Be<N<B<C\mathrm{Li}<\mathrm{Be}<\mathrm{N}<\mathrm{B}<\mathrm{C}

Answer: B

Step-by-step solution

First ionization enthalpy generally increases across a period due to increasing nuclear charge. However, Be has a higher ionization enthalpy than B because Be has a stable 2s² configuration, while B has a 2s²2p¹ configuration where the p-electron is easier to remove. The correct increasing order is: Li (520 kJ/mol) < B (801 kJ/mol) < Be (899 kJ/mol) < C (1086 kJ/mol) < N (1402 kJ/mol). Thus, the correct option is B.

Answer key and solution verified before publishing.

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Exam
NEET (UG) 2024
Paper
2024 paper
Subject
Chemistry
Chapter
Periodicity of Elements and Periodic Properties
Topic
Periodicity in Chemical Properties (Ionization Energy, Electron Affinity, Electronegativity)

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