Q49 / 180 · AIIMS 2015 · Chemistry

Assertion: $\mathrm{NF}_3$ is a weaker ligand than $\mathrm{N}\left(\mathrm{CH}_3\right)_3$. Reason : $\mathrm{NF}_3$ ionizes to give $\mathrm{F}^{-}$ions in aqueous solution.

  • A
    If both assertion and reason are true and reason is the correct explanation of assertion.
  • B
    Ifboth assertion and reason are true but reason is not the correct explanation of assertion.
  • Correct answer
    C
    If assertion is true but reason is false.
  • D
    If both assertion and reason are false.

Solution

Due to high electronegativity and electron withdrawing nature of $\mathrm{F}$-atom, the lone pair of $\mathrm{N}$-atom in $\mathrm{NF}_3$ molecule is not easily available for donation. Whereas in $\mathrm{N}\left(\mathrm{CH}_3\right)_3,-\mathrm{CH}_3$ group is an electron releasing group, thus lone pair of $\mathrm{N}$-atom in $\mathrm{N}\left(\mathrm{CH}_3\right)_3$ molecule can be ligated easily. Except, nitrogen fluoride, all other trihalides hydrolyse in water. $$ \mathrm{NCl}_3+3 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{NH}_3+3 \mathrm{HOCl} $$

Hence, the correct answer is option: 'C'.

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