Considering $\mathrm{H}_2 \mathrm{O}$ as weak field ligand, the number of unpaired electrons in $\left[\mathrm{Mn}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$ will be (Atomic number of $\mathrm{Mn}=25$ )

• Correct answer
  A

  five
• B

  two
• C

  four
• D

  three

Solution

Mn in $\left[\mathrm{Mn}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$ is present as $\mathrm{Mn}^{2+}\left(3 d^5\right)$. $s p^3 d^2$ hybridisation occurs in $\left[\mathrm{Mn}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}$. Due to the presence of weak field ligand pairing of electron does not take place, hence the number of unpaired electrons is five.

Hence, the correct answer is option: 'A'.