Which of the following ions is paramagnetic?

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(B) To determine if an ion is paramagnetic,we check for the presence of unpaired electrons in its electronic configuration.$1$. $O_2^{2-}$ (Peroxide i

Vedclass · Accepted Answer

$Cr^{3+}$

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(B) To determine if an ion is paramagnetic,we check for the presence of unpaired electrons in its electronic configuration.$1$. $O_2^{2-}$ (Peroxide ion): Total electrons = $8 + 8 + 2 = 18$. Configuration: $(\sigma 1s)^2, (\sigma^* 1s)^2, (\sigma 2s)^2, (\sigma^* 2s)^2, (\sigma 2p_z)^2, (\pi 2p_x)^2 = (\pi 2p_y)^2, (\pi^* 2p_x)^2 = (\pi^* 2p_y)^2$. All electrons are paired,so it is diamagnetic.$2$. $Cr^{3+}$: Atomic number of $Cr$ is $24$. Configuration of $Cr$ is $[Ar] 3d^5 4s^1$. $Cr^{3+}$ loses $3$ electrons: $[Ar] 3d^3$. It has $3$ unpaired electrons,so it is paramagnetic.$3$. $Na^+$: Atomic number $11$. Configuration: $1s^2 2s^2 2p^6$. All electrons are paired,so it is diamagnetic.$4$. $Cu^+$: Atomic number $29$. Configuration of $Cu$ is $[Ar] 3d^{10} 4s^1$. $Cu^+$ loses $1$ electron: $[Ar] 3d^{10}$. All electrons are paired,so it is diamagnetic.Therefore,$Cr^{3+}$ is the paramagnetic ion.

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