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JEE Mains Previous Years Questions with Solutions

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1

AIEEE 2006

MCQ (Single Correct Answer)
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.
2

AIEEE 2005

MCQ (Single Correct Answer)
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.
3

AIEEE 2004

MCQ (Single Correct Answer)
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.
4

AIEEE 2004

MCQ (Single Correct Answer)
Which one of the following has the regular tetrahedral structure?
(Atomic nos : B = 5, S = 16, Ni = 28, Xe = 54)
A
XeF4
B
[Ni(CN)4]2-
C
$$BF_4^-$$
D
SF4

Explanation

Regular Tetrahedral structure is possible in sp3 hybridization where central atom has 4 bond pair and no lone pair.

(a)   XeF4  is sp3d2 hybridised and structure is square planar.



(b)   [Ni(CN)4]$$-$$2 is coordinate compound and oxidation number of Ni is +2.

Electronic configuration of Ni+2 is $$=$$ [Ar]3d8



But because of CN$$-$$ ion which is a strong field ligand , it can perform pairing of electron.



And the structure of dsp2 hybridization is square planar.



(C) $$\,\,\,\,$$ BF$$_4^ - $$, 4 bond pair present so angle is 109o 28' and sp3 hybridised. So structure is regular tetrahedral.



(d)   

SF4 is sp3d hybridised and structure is see-saw.

Questions Asked from Chemical Bonding & Molecular Structure

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