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1

### AIPMT 2015 Cancelled Paper

Maximum bond angle at nitrogen is present in which of the following ?
A
NO2+
B
NO3$$-$$
C
NO2
D
NO2$$-$$

## Explanation

Species $$NO_3^-$$ $$NO_2$$ $$NO_2^-$$ $$NO_2^+$$
Hybridisation sp2 sp2 sp2 sp(linear)
Bond Angle 120o 134o 115o 180o
2

### AIPMT 2015 Cancelled Paper

Which of the following options represents the correct bond order ?
A
O2$$-$$  > O2 < O2+
B
O2$$-$$  <  O2  >  O2+
C
O2$$-$$  >  O2  >  O2+
D
O2$$-$$  <  O2  <  O2+

## Explanation

$$\,$$ Bond order $$= {1 \over 2}$$ [Nb $$-$$ Na]

Nb = No of electrons in bonding molecular orbital

Na $$=$$ No of electrons in anti bonding molecular orbital

In O atom 8 electrons present, so in O2, 8 $$\times$$ 2 = 16 electrons present.

Then in $$O_2^ +$$ no of electrons = 15

in $$O_2^ -$$ no of electrons = 17

$$\therefore\,\,\,\,$$ Molecular orbital configuration of O2 (16 electrons) is

$${\sigma _{1{s^2}}}\,\,\sigma _{1{s^2}}^ * \,$$ $${\sigma _{2{s^2}}}\,\,\sigma _{2{s^2}}^ * \,$$ $${\sigma _{2p_z^2}}\,\,{\pi _{2p_x^2}} = {\pi _{2p_y^2}}\,\,\pi _{2p_x^1}^ * \,\, = \pi _{2p_y^1}^ *$$

$$\therefore\,\,\,\,$$Na = 6

Nb = 10

$$\therefore\,\,\,\,$$ BO = $${1 \over 2}\left[ {10 - 6} \right] = 2$$

Molecular orbital configuration of O$$_2^ +$$ (15 electrons) is

$${\sigma _{1{s^2}}}\,\sigma _{1{s^2}}^ * \,{\sigma _{2{s^2}}}\,\sigma _{2{s^2}}^ * \,{\sigma _{2p_z^2}}\,{\pi _{2p_x^2}}\, = \,{\pi _{2p_y^2}}\,\pi _{2p_x^1}^ * \, = \,\pi _{2p_y^o}^ *$$

$$\therefore\,\,\,\,$$ Nb = 10

Na = 5

$$\therefore\,\,\,\,$$ BO = $${1 \over 2}\left[ {10 - 5} \right]$$ = 2.5

Molecular orbital configuration of $$O_2^ -$$ (17 electrons) is

$${\sigma _{1{s^2}}}\,\sigma _{1{s^2}}^ * \,{\sigma _{2{s^2}}}\,\sigma _{2{s^2}}^ * \,{\sigma _{2p_z^2}}\,{\pi _{2p_x^2}}\, = \,{\pi _{2p_y^2}}\,\pi _{2p_x^2}^ * \, = \,\pi _{2p_y^1}^ *$$

$$\therefore\,\,\,\,$$ Nb = 10

Na = 7

$$\therefore\,\,\,\,$$ BO = $${1 \over 2}\left[ {10 - 7} \right]$$ = 1.5

$$O_2^-$$ $$O_2$$ $$O_2^+$$
B.O. : 1.5 2.0 2.5
3

### AIPMT 2015

In which of the following pairs, both the species are not isostructural ?
A
Diamond, Silicon carbide
B
NH3, PH3
C
XeF4, XeO4
D
SiCl4, PCl4+

## Explanation

4

### AIPMT 2014

Which one of the following species has plane triangular shape ?
A
N3
B
NO3$$-$$
C
NO2$$-$$
D
CO2

## Explanation

Hybridisation of N3 is sp, so it is linear in shape.

Hybridisation of NO3 is sp2, so it is plane triangular in shape.

Hybridisation of NO2 is sp, so it is linear in shape.

Hybridisation of CO2 is sp, so it is linear in shape.

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