The number of molecule(s) or ion(s) from the following having non-planar structure is ____________.
NO₃⁻, H₂ O₂, BF₃, PCl₃, XeF₄, SF₄, XeO₃, PH₄⁺, SO₃,[Al(OH)₄]⁻

Solution

Chemistry ma’am · 3 steps

Find each shape from bond pairs and lone pairs, then ask if every atom can lie in one flat sheet.

1. Count the pairs. For each central atom, count bond pairs and lone pairs. VSEPR gives the shape, and the shape tells you if all the atoms can share one plane.

   Species	Bond pairs, lone pairs	Shape	Planar?
   NO₃⁻, BF₃, SO₃	3, 0	trigonal planar	yes
   XeF₄	4, 2	square planar (lone pairs opposite each other)	yes
   PCl₃, XeO₃	3, 1	trigonal pyramidal	no
   SF₄	4, 1	see-saw	no
   PH₄⁺, [Al(OH)₄]⁻	4, 0	tetrahedral	no
   H₂O₂	2, 2 on each O	open book, the two O–H bonds twisted out of one plane	no

2. Watch two cases. In XeF₄ the two lone pairs sit above and below, so the four F atoms stay flat around Xe. In SF₄ one lone pair takes an equatorial position, which bends the molecule into a see-saw.
3. So. The non-planar ones are H₂O₂, PCl₃, SF₄, XeO₃, PH₄⁺ and [Al(OH)₄]⁻, a total of 6.

The common slip: 7. Counting XeF₄ as non-planar because of its sp³d² hybridisation gives 7. Its two lone pairs sit opposite each other, so all five atoms lie in one plane.

The idea to keep. Planarity comes from the shape, not the hybridisation alone. Lone pairs placed opposite each other keep a molecule flat, as in XeF₄. A single lone pair usually pushes the atoms out of plane.

Answer from the NTA final answer key. Solution by PrepWiser.