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1

### AIPMT 2014

Which of the following molecules has the maximum dipole moment ?
A
CO2
B
CH4
C
NH3
D
NF3

## Explanation

Even though for CO2 and CH4 the C - O and C - H bonds are polar but due to their symmetrical structure they have zero dipole moment.
In NH3, H is less electronegative than N and hence the dipole moment of each N-H bond is towards N which is in the similar direction of lone pair but for NF3 the dipole moment of N-F bond is in opposite direction of lone pair which reduce the value of net dipole moment.
2

### NEET 2013

Identify the correct order of solubility in aqueous medium.
A
Na2S > CuS > ZnS
B
Na2S > ZnS > CuS
C
Cus > ZnS > Na2S
D
ZnS > Na2S > CuS

## Explanation

Water is a polar compound so the salt which is more polar or having more ionic character will be more soluble in it. According to Fajan's rule, ionic character of compound increases with increase in the size of cation. Now, among the given compounds, the size of cations are in the order as follows :

Na+ > Zn2+ > Cu2+

Thus, the order of ionic character and the solubility order in aqueous medium is as follows :

Na2S > ZnS > CuS
3

### NEET 2013 (Karnataka)

In which of the following ionization processes the bond energy increases and the magnetic behaviour changes from paramagnetic to diamagnetic.
A
O2 $$\to$$ O2+
B
C2 $$\to$$ C2+
C
NO $$\to$$ NO+
D
N2 $$\to$$ N2+

## Explanation

Molecular orbital configuration of

O2+ $$\Rightarrow$$ $$\sigma 1{s^2}{\sigma ^*}1{s^2}\sigma 2{s^2}{\sigma ^*}2{s^2}\sigma 2p_z^2\pi 2p_y^2{\pi ^*}2p_x^1{\pi ^*}2p_y^1$$ $$\Rightarrow$$ Paramagnetic

Bond order = $${{10 - 5} \over 2} = 2.5$$

C2 $$\Rightarrow$$ $$\sigma 1{s^2}{\sigma ^*}1{s^2}\sigma 2{s^2}{\sigma ^*}2{s^2}\sigma 2p_z^2\pi 2p_y^2$$ $$\Rightarrow$$ Diamagnetic

Bond order = $${{8 - 4} \over 2} = 2$$

C2+ $$\Rightarrow$$ $$\sigma 1{s^2}{\sigma ^*}1{s^2}\sigma 2{s^2}{\sigma ^*}2{s^2}\sigma 2p_z^2\pi 2p_y^1$$ $$\Rightarrow$$ Paramagnetic

Bond order = $${{7 - 4} \over 2} = 1.5$$

NO $$\Rightarrow$$ $$\sigma 1{s^2}{\sigma ^*}1{s^2}\sigma 2{s^2}{\sigma ^*}2{s^2}\sigma 2p_z^2\pi 2p_y^2{\pi ^*}2p_x^1$$ $$\Rightarrow$$ Paramagnetic

Bond order = $${{10 - 5} \over 2} = 2.5$$

NO+ $$\Rightarrow$$ $$\sigma 1{s^2}{\sigma ^*}1{s^2}\sigma 2{s^2}{\sigma ^*}2{s^2}\sigma 2p_z^2\pi 2p_x^2\pi 2p_y^2$$ $$\Rightarrow$$ Diamagnetic

Bond order = $${{10 - 4} \over 2} = 3$$

N2 $$\Rightarrow$$ $$\sigma 1{s^2}{\sigma ^*}1{s^2}\sigma 2{s^2}{\sigma ^*}2{s^2}\pi 2p_x^2\pi 2p_y^2\sigma 2p_z^2$$ $$\Rightarrow$$ Paramagnetic

Bond order = $${{10 - 4} \over 2} = 3$$

N2+ $$\Rightarrow$$ $$\sigma 1{s^2}{\sigma ^*}1{s^2}\sigma 2{s^2}{\sigma ^*}2{s^2}\pi 2p_x^2\pi 2p_y^2\sigma 2p_z^1$$ $$\Rightarrow$$ Paramagnetic

Bond order = $${{9 - 4} \over 2} = 2.5$$
4

### NEET 2013 (Karnataka)

The outer orbitals of C in ethane molecule can be considered to be hybridized to give three equivalent sp2 orbitals. The total number of sigma $$\left( \sigma \right)$$ and pi $$\left( \pi \right)$$ bonds in ethane molecule is
A
3 sigma $$\left( \sigma \right)$$ and 2 pi $$\left( \pi \right)$$ bonds
B
4 sigma $$\left( \sigma \right)$$ and 1 pi $$\left( \pi \right)$$ bonds
C
5 sigma $$\left( \sigma \right)$$ and 1 pi $$\left( \pi \right)$$ bonds
D
1 sigma $$\left( \sigma \right)$$ and 2 pi $$\left( \pi \right)$$ bonds

## Explanation

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Class 12