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JEE Main levelSingle correct optionDifficulty 2 of 3sb018

Which of the following compounds is paramagnetic?

A $KO X_{2}$
B $BaO$
C $Na X_{2} O X_{2}$
D $Li X_{2} O$

Answer: A

The superoxide ion

O X_{2} X^{-}

has one unpaired electron in a

π^{*}

orbital, so

KO X_{2}

is paramagnetic. The peroxide ion

O X_{2} X^{2 -}

and the oxide ion have all electrons paired, so

Na X_{2} O X_{2}

,

Li X_{2} O

and

BaO

are diamagnetic.

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