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1

### 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
2

### 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
3

### AIPMT 2011 Mains

The pairs of species of oxygen and their magnetic behaviours are noted below. Which of the following presents the correct description?
A
$$O_2^ - ,O_2^{2 - }$$ - Both diamagnetic
B
$$O_2^ + ,{O_2}$$ - Both paramagnetic
C
O, $$O_{2}^{2-}$$ - Both paramagnetic
D
$${O^ + },O_2^{2 - }$$ - Both paramagnetic

## Explanation

O2+ = KKσ2s2 σ*2s2 σ2pz2 (π2px2 = π2py2) (π*2px1)

O2 = KKσ2s2 σ*2s2 σ2pz2 (π2px2 = π2py2) (π*2px 1 = π*2py1)

O2 and O2+ contain unpaired electron in π* ABMO so paramagnetic.
4

### AIPMT 2011 Mains

Which of the following structures is the most preferred and hence of lowest energy for SO3?
A
B
C
D

## Explanation

has maximum number of covalent bonds.

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