Question

Which one of the following complex or ion is paramagnetic?

• A. $Ni(CO{)}_4$
• B. $K_4\left[Fe\right(CN{)}_6]$
• C. $\left[Cr\right({N{H}_3)}_6{]}^{3+}$
• D. $\left[Ni\right(CN{)}_4{]}^{2-}$

Answer 1

The correct option is C $\left[Cr\right({N{H}_3)}_6{]}^{3+}$

$\left[Cr\right(N{H}_3{)}_6{]}^{3+}$

$-24Cr⟶4s^{1}3d^5$

$C{r}^{3+}⟶4s^{0}3d^3$

(Refer to Image 1)

$N{H}_3$ being weak ligand, pairing of $e^{-}s$ does not occur.

$\left[Cr\right(N{H}_3{)}_6{]}^{3+}\Rightarrow$ (Refer to Image 2)

$3$ unpaired $e^{-}s$ are present

$\therefore$ It is paramagnetic.

Anwer is option C.