Question

Which of the following has highest para-magnetism?
${\left[Zn{\left(H_{2}O\right)}_4\right]}^{2+},{\left[Cr{\left(H_{2}O\right)}_6\right]}^{3+},{\left[Fe{\left(H_{2}O\right)}_6\right]}^{3+},{\left[Cu{\left(H_{2}O\right)}_4\right]}^{2+}$

Answer 1

$\left[Zn\right(H_{2}O{)}_4{]}^{2+}$

$Z{n}^{2+}$ $4s^{0}3d^{10}$

All the $e^{-}s$ in 3d are paired. $\therefore$ dimagnetic.

$\left[Cr\right(H_{2}O{)}_6{]}^{3+}$

$C{r}^{3+}:4s^{0}3d^3⟶3$ unpaired $e^{-}$ in 3d.

$\left[Fe\right(H_{2}O{)}_6{]}^{3+}$

$F{e}^{3+}:4s^{0}3d^5⟶5$ unpaired $e^{-}$.

$\left[Cu\right(H_{2}O{)}_4{]}^{2+}$

$C{u}^{2+}:4s^{0}3d^9⟶1$ unpaired $e^{-}$.

More is the number of unpaired $e^{-}$ higher is the paramagnetism.

$\therefore \left[Fe\right(H_{2}O{)}_6{]}^{3+}$ has highest para magnetism.