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JEE Main levelSingle correct optionDifficulty 2 of 3sb125

Assertion (A): $KO X_{2}$ is paramagnetic. Reason (R): The superoxide ion $O X_{2} X^{-}$ has two unpaired electrons.

ABoth A and R are true and R is the correct explanation of A
BBoth A and R are true but R is not the correct explanation of A
CA is true but R is false
DA is false but R is true

Answer: C

O X_{2} X^{-}

has 17 valence-level electrons in the MO picture, giving the configuration

σ_{2 p}^{2} π_{2 p}^{4} π_{2 p}^{* 3}

, which has just one unpaired electron. So A is true (paramagnetic) but R is false because two unpaired electrons occur in

O X_{2}

, not

O X_{2} X^{-}

.

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