1
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 $$O_2^+$$
2
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

3
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
4
MCQ (Single Correct Answer)

AIPMT 2012 Prelims

Which one of the following pairs is isostructural (i.e., having the same shape and hybridization) ?
A
[BCl3 and BrCl3]
B
[NH3 and NO$$_3^ - $$]
C
[NF3 and BF3]
D
[BF$$_4^ - $$ and NH$$_4^ + $$]

Explanation

BCl3 $$ \Rightarrow $$ sp2, trigonal planar

BrCl3 $$ \Rightarrow $$ sp3d, T-shaped

NH3 $$ \Rightarrow $$ sp3, pyramidal

NO3- $$ \Rightarrow $$ sp2, trigonal planar

NF3 $$ \Rightarrow $$ sp3, pyramidal

BF3 $$ \Rightarrow $$ sp2, trigonal planar

BF4- $$ \Rightarrow $$ sp3, tetrahedral

NH4- $$ \Rightarrow $$ sp3, tetrahedral

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