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Which of the following molecules has trigonal planar geometry :
A
$NH_3$
B
$BF_3$
C
$PCl_3$
D
$IF_3$
Detailed Solution
$BF_3$: boron has three valence electrons and forms three B-F bonds with no lone pair. It is $sp^2$ hybridised, so the molecule is trigonal planar with bond angles of $120^\circ$.
$NH_3$: three bond pairs and one lone pair on nitrogen ($sp^3$), so it is trigonal pyramidal.
$PCl_3$: three bond pairs and one lone pair on phosphorus, so it is also trigonal pyramidal.
$IF_3$: three bond pairs and two lone pairs on iodine ($sp^3d$), so it is T-shaped.
So the molecule with trigonal planar geometry is $BF_3$.
$NH_3$: three bond pairs and one lone pair on nitrogen ($sp^3$), so it is trigonal pyramidal.
$PCl_3$: three bond pairs and one lone pair on phosphorus, so it is also trigonal pyramidal.
$IF_3$: three bond pairs and two lone pairs on iodine ($sp^3d$), so it is T-shaped.
So the molecule with trigonal planar geometry is $BF_3$.