1

### AIPMT 2007

Which of the following oxidation states are the most characteristic for lead and tin respectively?
A
+2, +4
B
+4, +4
C
+2, +2
D
+4, +2

## Explanation

The tendency to from +2 ionic state increases on moving down the group due to inert pair effect. Most characteristic oxidation state for lead and tin are +2, +4 respectively.
2

### AIPMT 2006

In which of the following molecules are all the bonds are not equal?
A
NF3
B
ClF3
C
BF3
D
AlF3

## Explanation

The Cl - F (Cl - Fb) bond length is equal to 1.60 $\mathop A\limits^o$ while each of two axial Cl - F (Cl - Fa) bond length is equal to 1.70 $\mathop A\limits^o$.
3

### AIPMT 2006

Which one of the following orders is not in accordance with the property stated against it?
A
F2 > Cl2 > Br2 > I2 : Bond dissociation energy
B
F2 > Cl2 > Br2 > I2 : Oxidising power
C
HI > HBr > HCl > HF : Acidic property in water
D
F2 > Cl2 > Br2 > I2 : Electronegativity.

## Explanation

Bond dissociation energy is kcal/mol of F - F, Cl - Cl, Br - Br and I - I are 38, 57, 45.5 and 35.6 respectively.

Bond dissociation energy of fluorine is less because of its small size and repulsion between electrons of two atoms.
4

### AIPMT 2006

The electronegativity difference berween N and F is greater than that between N and H yet the dipole moment of NH3 (1.5D) is larger than that of NF3 (0.2 D). This is because
A
in NH3 the atomic dipole and bond dipole are in the opposite directions whereas in NF3 these are in the same direction
B
in NH3 as well as in NF3 the atomic dipole and bond dipole are in the same direction
C
in NH3 the atomic dipole and bond dipole are in the same direction whereas in NF3 these are in opposite directions
D
in NH3 as well as in NF3 the atomic dipole and bond dipole are in opposite directions.

## Explanation

The dipole moment of NF3 is 0.24 D and of NH3 is 1.48 D. In NF3, the dipole moment vector are aligned in opposite direction to that of the dipole moment vector of lone pair on N–atom which partly cancel out. On the other hand, N–H bonds in NH3 are in the same direction of dipole moment of the lone pair on N-atom which adds up the new resultant dipole moment.

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