1
MCQ (Single Correct Answer)

AIPMT 2012 Mains

Four diatomic species are listed below. Identify the correct order in which the bond order is increasing in them
A
$$NO < {O_2}^ - < {C_2}^{2 - } < He_2^ + $$
B
$${O_2}^ - < NO < {C_2}^{2 - } < He_2^ + $$
C
$${C_2}^{2 - } < He_2^ + < {O_2}^ - < NO$$
D
$$He_2^ + < {O_2}^ - < NO < {C_2}^{2 - }$$

Explanation

Diatomic species Bond order
NO 2.5
$$O_2^-$$ 1.5
$$C_2^{2-}$$ 3.0
$$He_2^+$$ 0.5
The increasing order: $$He_2^ + < {O_2}^ - < NO < {C_2}^{2 - }$$
2
MCQ (Single Correct Answer)

AIPMT 2012 Mains

During change of O2 to O$$_2^{ - }$$ ion, the electron adds on which one of the following orbitals ?
A
$${\pi ^ * }$$ orbital
B
$$\pi $$ orbital
C
$${\sigma ^ * }$$ orbital
D
$$\sigma $$ orbital

Explanation

Electronic configuration of O2

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

Thus the incoming electron will enter in $$\pi ^*2p_x$$ to form $$O_2^+$$
3
MCQ (Single Correct Answer)

AIPMT 2012 Prelims

Which of the following species contains three bond pairs and one lone pair arround the central atom ?
A
H2O
B
BF3
C
NH2$$-$$
D
PCl3

Explanation

4
MCQ (Single Correct Answer)

AIPMT 2012 Prelims

Bond order of 1.5 is shown by
A
O2+
B
O2$$-$$
C
O22$$-$$
D
O2

Explanation

Configuration of O2

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

Bond order = $${{No.\,of\,{e^ - }\,in\,bonding\,M.O - No.\,of\,{e^ - }\,in\,antibonding\,M.O} \over 2}$$

Bond order of O2+ = $${{10 - 5} \over 2}$$ = 2.5

Bond order of O2- = $${{10 - 7} \over 2}$$ = 1.5

Bond order of O22- = $${{10 - 8} \over 2}$$ = 1

Bond order of O2 = $${{10 - 6} \over 2}$$ = 2

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