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1

### AIPMT 2005

Which of the following molecules has trigonal planar geometry?
A
BF3
B
NH3
C
PCl3
D
IF3

## Explanation

IF3 has three bond pairs and two lone pairs, thus, it has sp3d hybridization.

PCl3 has three bond pairs and one lone pair thus, it has sp3 hybridization.

NH3 has three bond pairs and one lone pair thus, it has sp3 hybridisation.

BF3 has three bond pairs and no lone pair thus, it has sp2 hybridisation.
2

### AIPMT 2005

The correct order in which the O $$-$$ O bond length increases in the following is
A
O2 < H2O2 < O3
B
O3 < H2O2 < O2
C
H2O2 < O2 < O3
D
O2 < O3 < H2O2

## Explanation

Bond lengths of O $$-$$ O in O2 is 1.21 Å, in H2O2 is 1.48 Å and in O3 is 1.28Å. Therefore, correct order of the O $$-$$ O bond length is H2O2 > O3 > O2 or O2 < O3 < H2O2
3

### AIPMT 2004

In BrF3 molecule, the lone pairs occupy equatorial positions to minimize
A
lone pair - bond pair repulsion only
B
bond pair - bond pair repulsion only
C
lone pair - lone pair repulsion and lone pair - bond pair repulsion
D
lone pair - lone pair repulsion only.

## Explanation

Lone pair - Lone pair repulsion > lone pair - bond pair repulsion > bond pair-bond pair repulsion.

The lone pairs of electrons are arranged on equatorial position as they are at maximum distance at these positions and hence they have minimum repulsion at these positions.
4

### AIPMT 2004

H2O is dipolar, whereas BeF2 is not. It is because
A
the electronegativity of F is greater than that of O
B
H2O involves hydrogen bonding whereas BeF2 is a discrete molecule
C
H2O is linear and BeF2 is angular
D
H2O is angular and BeF2 is linear.

## Explanation

In H2O the central atom oxygen has two lone pairs of electrons and two bond pairs of electrons. Thus, the shape of H2O is bent or V-shape. Thus, the two dipoles of H-O bonds have some resultant value as they are not exactly in the opposite direction to cancel out each other. While in BeF2, there are two bond pairs on central atom Be, hence it is linear in shape. Thus, the two dipoles of bonds are exactly in opposite direction to each other and cancel each other to give net zero dipole moment.

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