According to VBT, number of unpaired electrons are least in the complex

• A

  ${\left[\mathrm{Mn}{\left(\mathrm{CN}\right)}_6\right]}^{-3}$

• B

  ${\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{+2}$

• C

  ${\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]}^{-3}$

• D

  ${\left[\mathrm{Cr}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{+3}$