Considering $\mathrm{H}_2 \mathrm{O}$ as a 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 $\mathrm{Mn}=25$ )

• A

  three
• Correct answer
  B

  five
• C

  two
• D

  four

Solution

$\mathrm{H}_2 \mathrm{O}$ is a weak ligand. Thus, there will be no pairing of electron and forms high spin complex. Thus, no. of unpaired $e^{-}=5$ Related Theory $\left[\mathrm{Mn}\left(\mathrm{H}_2 \mathrm{O}\right)\right]^{2+}$ has octahedral geometry where the central atom are surrounded by 6 other molecules or ligands that are systematically arranged.

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