### JEE Mains Previous Years Questions with Solutions

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1

### AIEEE 2006

In which of the following molecules/ions are all the bonds not equal?
A
XeF4
B
$BF_4^−$
C
SF4
D
SiF4

## Explanation

(a)   XeF4  is sp3d2 hybridised with 4 bond pairs and 1 lone pair and structure is square planar. Here all the bond lengths are equal.

(b) $\,\,\,\,$ BF$_4^ -$, 4 bond pair present so angle is 109o 28' and sp3 hybridised. So structure is regular tetrahedral. Here all the bond lengths are equal.

(c)   SF4 is sp3d hybridised with 4 bond pairs and 1 lone pair and its expected trigonal bipyramidal geometry gets distorted due to presence of a lone pair of electrons and it becomes distorted tetrahedral or see-saw with the bond angles equal to < 120o and 179o instead of the expected angles of 120o and 180o respectively. Here axial and equitorial both bonds are presents. And we know axial bonds are longer and weaker.

(d) SiF4 is sp3 hybridisation and regular tetrahedral geometry. Here all the bond lengths are equal.

2

### AIEEE 2006

Which of the following molecules/ions does not contain unpaired electrons?
A
$O_2^{2−}$
B
B2
C
$N_2^+$
D
O2

## Explanation

(A) Molecular orbital configuration of O $_2^{2 - }$ (18 electrons) is

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

So O $_2^{2 - }$ has no unpaired electrons.

(B) Molecular orbital configuration of B2 (10 electrons) is

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

Here in B2, 2 unpaired electrons present.

(C) Moleculer orbital configuration of $N_2^{ + }$ (13 electrons)

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

Here in $N_2^{ + }$, 1 unpaired electron present,

(D) Molecular orbital configuration of O2 (16 electrons) is

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

So O$_2$ has 2 unpaired electrons.
3

### AIEEE 2005

Lattice energy of an ionic compounds depends upon
A
Charge on the ion only
B
Size of the ion only
C
Packing of ions only
D
Charge on the ion and size of the ion

## Explanation

Electrostatic force of attraction between cation and anion is called Lattice energy.

Lattice energy (F) = $K{{{q_1}{q_2}} \over {{r^2}}}$

q1 and q2 are the charges of cations and anion. So Lattice energy depens on the charges of ions.

r = distance between center of ions

And, r = r+ + r- where r+ = radius of cation and r- = radius of anion

So, more the size of ions less the value of Lattice energy.
4

### AIEEE 2004

The maximum number of 90° angles between bond pair of electrons is observed in
A
dsp3 hybridization
B
sp3d2 hybridization
C
dsp2 hybridization
D
sp3d hybridization

## Explanation

Here eight 90o angles between bond pair and bond pair. Those angles are $\angle$1M2, $\angle$2M3, $\angle$3M4, $\angle$4M1, $\angle$5M1, $\angle$5M2, $\angle$5M3, $\angle$5M4.

Here twelve 90o angles between bond pair and bond pair. Those angles are $\angle$1M2, $\angle$2M3, $\angle$3M4, $\angle$4M1, $\angle$5M1, $\angle$5M2, $\angle$5M3, $\angle$5M4, $\angle$6M1, $\angle$6M2, $\angle$6M3, $\angle$6M4.

Here four 90o angles between bond pair and bond pair. Those angles are $\angle$1M2, $\angle$2M3, $\angle$3M4, $\angle$4M1.

Here six 90o angles between bond pair and bond pair. Those angles are $\angle$1M3, $\angle$1M4, $\angle$1M5, $\angle$2M3, $\angle$2M4, $\angle$2M5.