Concept:Iso-structural molecules share the exact same geometric shape, which usually implies having the same steric number and number of lone pairs on the central atom.
Formula:$$ \text{Shape of AB}_3 (\text{no lone pairs}) = \text{Trigonal Planar} $$
Solution:- In Sulfur trioxide (\( \text{SO}_3 \)), Sulfur forms 3 double bonds with oxygen and has 0 lone pairs (\( \text{sp}^2 \)). Geometry: Trigonal Planar.
- In Boron trifluoride (\( \text{BF}_3 \)), Boron forms 3 single bonds with fluorine and has 0 lone pairs (\( \text{sp}^2 \)). Geometry: Trigonal Planar.
- Because both molecules adopt the exact same flat, triangular geometry, they are iso-structural.
Why other options are incorrect:- Option A: \( \text{AlCl}_3 \) is planar, \( \text{CH}_4 \) is tetrahedral.
- Option B: \( \text{BF}_3 \) is planar, \( \text{NH}_3 \) is pyramidal (has a lone pair).
- Option C: \( \text{SnCl}_2 \) is bent (has a lone pair), \( \text{BeCl}_2 \) is linear.
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