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The fall in bond angle from NH3 (106°) to SbH3 (101°) as we move down group 15 is mainly because of
- a reduction in lone pair–bond pair repulsion
- a decrease in electronegativity
- an increase in bond pair–bond pair repulsion
- greater p-orbital character in sp3 hybridization
Correct answer: a decrease in electronegativity
Solution
Going N -> P -> As -> Sb, the central atom's electronegativity falls, so the bonding electron pairs lie farther from the central atom and closer to the H atoms. This reduces bond pair-bond pair repulsion near the centre, allowing the lone pair to push the bonds closer together, so the H-X-H angle decreases.
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