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1

### NEET 2013

Which of the following is paramagnetic?
A
CN$$-$$
B
NO+
C
CO
D
O2$$-$$

## Explanation

$$O_2^-$$ superoxide has one unpaired electron.
2

### NEET 2013

Dipole-induced dipole interactions are present in which of the following pairs
A
HCl and He atoms
B
SiF4 and He atoms
C
H2O and alcohol
D
Cl2 and CCl4

## Explanation

HCl is polar ($$\mu$$ $$\ne$$ 0) and He is non-polar ($$\mu$$ = 0) gives dipole-induced dipole interaction.
3

### NEET 2013 (Karnataka)

The pair of species that has the same bond order in the following is
A
CO, NO+
B
NO$$-$$, CN$$-$$
C
O2, N2
D
O2, B2

## Explanation

CO = + 8 = 14 electrons
NO+ = 7 + 8 - 1 = 14 electrons
Both have electronic configuration:
$$\sigma 1s^2$$ $$\sigma^* 1s^2$$ $$\sigma 2s^2$$ $$\sigma^* 2s^2$$ $$\sigma 2p_z^2$$ $$\sigma 2p_x^2$$ $$\sigma 2p_y^2$$
Bond order = $$10 - 4 \over 2$$ = 3
4

### NEET 2013

Which of the following is a polar molecule?
A
SiF4
B
XeF4
C
BF3
D
SF4

## Explanation

The given molecules SiF4, XeF4, and BF3 are symmetric molecules that is why due to cancellation of bond dipoles they are non-polar even though they contain polar bonds.

But in SiF4 there are four Si—F bonds and one lone pair due to which its structure is unsymmetrical. Hence, it is a polar molecule.

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Class 12