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Chemistry · Periodicity of Elements and Periodic Properties

JEE Main 2026 — 23 January, Morning Shift — Question 51

The correct trend in the first ionization enthalpies of the elements in the 3rd 3^{\text {rd }} period of periodic table is:

  1. Option A:

    Al<Si<S<P<Cl\mathrm{Al}<\mathrm{Si}<\mathrm{S}<\mathrm{P}<\mathrm{Cl}

    Correct
  2. Option B:

    Al<S<P<Si<Cl\mathrm{Al}<\mathrm{S}<\mathrm{P}<\mathrm{Si}<\mathrm{Cl}

  3. Option C:

    Si<S<Al<P<Cl\mathrm{Si}<\mathrm{S}<\mathrm{Al}<\mathrm{P}<\mathrm{Cl}

  4. Option D:

    S<Si<Al<P<Cl\mathrm{S}<\mathrm{Si}<\mathrm{Al}<\mathrm{P}<\mathrm{Cl}

Answer: A

Step-by-step solution

Across the 3rd period, first ionization enthalpy generally increases due to increase in effective nuclear charge.

However there are two exceptions:

Al\mathrm{Al} has lower value than Mg\mathrm{Mg} because electron is removed from 3p3p orbital.

S\mathrm{S} has lower value than P\mathrm{P} because P\mathrm{P} has half-filled 3p33p^3 configuration which is extra stable.

Thus, among the given elements the correct trend is Al<Si<S<P<Cl\mathrm{Al < Si < S < P < Cl}.

Hence, the option A is correct.

Answer key and solution verified before publishing.

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Exam
JEE Main 2026
Paper
23 January, Morning Shift
Subject
Chemistry
Chapter
Periodicity of Elements and Periodic Properties
Topic
Periodicity in Chemical Properties (Ionization Energy, Electron Affinity, Electronegativity)

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