Given below are two statements :

Statement I :

The number of species among $\mathrm{SF}_4, \mathrm{NH}_4^{+},\left[\mathrm{NiCl}_4\right]^{2-}, \mathrm{XeF}_4,\left[\mathrm{PtCl}_4\right]^{2-}, \mathrm{SeF}_4$ and $\left[\mathrm{Ni}(\mathrm{CN})_4\right]^{2-}$, that have tetrahedral geometry is 3 .

Statement II :

In the set [$\mathrm{NO}_2, \mathrm{BeH}_2, \mathrm{BF}_3, \mathrm{AlCl}_3$], all the molecules have incomplete octet around central atom.

In the light of the above statements, choose the correct answer from the options given below:

Question

Given below are two statements :

Statement I :

The number of species among $\mathrm{SF}_4, \mathrm{NH}_4^{+},\left[\mathrm{NiCl}_4\right]^{2-}, \mathrm{XeF}_4,\left[\mathrm{PtCl}_4\right]^{2-}, \mathrm{SeF}_4$ and $\left[\mathrm{Ni}(\mathrm{CN})_4\right]^{2-}$, that have tetrahedral geometry is 3 .

Statement II :

In the set [$\mathrm{NO}_2, \mathrm{BeH}_2, \mathrm{BF}_3, \mathrm{AlCl}_3$], all the molecules have incomplete octet around central atom.

In the light of the above statements, choose the correct answer from the options given below:

Accepted Answer

B. 1. For Statement I, check each species' actual geometry: SF₄ (see-saw), NH₄⁺ (tetrahedral), $[\mathrm{NiCl}_4]^{2-}$ (tetrahedral, since Ni²⁺ with weak-field Cl⁻ ligands stays d⁸ high-spin tetrahedral), XeF₄ (square planar), $[\mathrm{PtCl}_4]^{2-}$ (square planar, d⁸ with strong crystal field), SeF₄ (see-saw), $[\mathrm{Ni(CN)}_4]^{2-}$ (square planar, since CN⁻ is a strong-field ligand causing pairing).

2. Count only the truly tetrahedral species: NH₄⁺ and $[\mathrm{NiCl}_4]^{2-}$, giving a count of 2, not 3 as claimed.

3. Since the actual count is 2, Statement I is false.

4. For Statement II, check each molecule for incomplete octet: NO₂ (odd-electron molecule, N cannot complete octet), BeH₂ (only 4 electrons around Be), BF₃ (only 6 electrons around B), AlCl₃ (only 6 electrons around Al in its monomeric form).

5. Since all four molecules indeed have incomplete octets around their central atoms, Statement II is true.

Hence, Statement I is false but Statement II is true, so the answer is option B.