### JEE Mains Previous Years Questions with Solutions

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1

### AIEEE 2003

The pair of species having identical shapes for molecules of both species is
A
XeF2, CO2
B
BF3, PCl3
C
PF5, IF5
D
CF4, SF4

## Explanation

2

### AIEEE 2003

Which one of the following compounds has the smallest bond angle in its molecule?
A
OH2
B
SH2
C
NH3
D
SO2

## Explanation

(a)   H2O is sp3 hybridized, and oxygen atom has 2 bond pair and 2 lone pair. So the angle between two O $-$ H bond is 104.5o

(b)   In H2S molecule, central atom S is a 3rd period element and according to Dragos rule, when a 3rd period or higher period element overlap with a small element whose electronegetivity is low then that over lapping cannot be a effective overlapping, because of higher size of 3rd or higher periods element and smaller size of low electronegative element.

Here in H2S, H atom has very low electronegativity and smaller in size so it create more negative charge around sulphur(s) atom and size of S$-$2 ion increases, because of this higher size difference efficiency overlapping is not possible. So, any hybridization do not happen in between S and H atom. Lone pair electrons of S atom is present in the pure orbital like s, px, py, pz and it look like this :

As we know the angle between and py is 90o, so bond angle is 90o.

(c)   NH3 has sp3 hybridization and N atom has 3 bond pair and one lone pair so bond angle is 107o

(d)   SO2 is sp2 hybridized and bond angle is 117o.

3

### AIEEE 2003

Which one of the following pairs of molecules will have permanent dipole moments for both members
A
NO2 and CO2
B
NO2 and O3
C
SiF4 abd CO2
D
SiF4 abd NO2

## Explanation

Here $\mu$total = $\mu$1 + $\mu$2 $\ne$ 0

$\mu$total = $\mu$1 $-$ $\mu$2 = 0

$\mu$total = $\mu$1 + $\mu$2 $\ne$ 0

$\mu$1 + $\mu$2 + $\mu$3 = $\mu$4

$\mu$total = 0

In NO2 and O3 have permanent dipole moment as both of them are not symmetric molecule.

In CO2 and SiF4 each individual bond c = O and S- $-$ F have dipole moment but because of symmetric structure individual dipole moment get's cancelled.
4

### AIEEE 2003

An ethar is more volatile than an alcohol having the same molecular formula. This is due to
A
alcohols having resonance structures
B
inter-molecular hydrogen bonding in ethers
C
inter-molecular hydrogen bonding in alcohols
D
dipole characters of ethers

## Explanation

Alcohol and ether are isomer with each other. So, with same molecular formula we can make ether as well as alcohol.

For ex,

With molecular formula C2H6O

(1) $\,\,\,$ alcohol will be CH3CH2 OH

(2) $\,\,\,$ ether will be CH3 $-$ O $-$ CH3

In Alcohol there is hydrogen bond and in Ether there is Van der walls force of attraction.

We know that H bond is stronger bond than van der walls force of attraction as the atoms of alcohol are strongly attached with each other by hydrogen bonding so tendency of vaporization of alcohol is less compared to ether.

In alcohol inter-molecular hydrogen bonding look like this -

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