JEE Main · 2021 · Shift-ImediumIEQ-003

Which of the following compound CANNOT act as a Lewis base?

Ionic Equilibrium · Class 11 · JEE Main Previous Year Question

Question

Which of the following compound CANNOT act as a Lewis base?

Options
  1. a

    NF3\mathrm{NF_3}

  2. b

    PCl5\mathrm{PCl_5}

  3. c

    SF4\mathrm{SF_4}

  4. d

    ClF3\mathrm{ClF_3}

Correct Answerb

PCl5\mathrm{PCl_5}

Detailed Solution

Lewis base = electron pair donor (must have a lone pair available for donation).

Step 1 — Analyse each compound:

(1) NF3\mathrm{NF_3}: N has a lone pair \rightarrow can donate \rightarrow Lewis base ✓ (though weakly, due to F withdrawing electrons)

(2) PCl5\mathrm{PCl_5}: P has 5 bonds, no lone pairs, and an empty d-orbital \rightarrow acts as Lewis acid (electron acceptor), NOT a Lewis base ✗

(3) SF4\mathrm{SF_4}: S has one lone pair \rightarrow can donate \rightarrow Lewis base

(4) ClF3\mathrm{ClF_3}: Cl has two lone pairs \rightarrow can donate \rightarrow Lewis base

Answer: Option (2) — PCl5\mathrm{PCl_5}

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Which of the following compound CANNOT act as a Lewis base? (JEE Main 2021) | Canvas Classes