In hexacyanomanganate (II) ion, the $Mn$ atom assumes a $d^{2}s{p}^3-$ hybrid state. The number of unpaired electrons in the complex is:

The correct option is D 1
Ground state electronic configuration of $Mn\left(II\right):3d^5,4s^0$
Since cyano is a strong field ligand, it will cause pairing in $3d$ orbitals leaving two $3d$ orbitals vacant.
Now the six ligands occupy the next empty orbital leading to $d^{2}s{p}^3$ hybridisation.
So only one electron remains unpaired in the $3d$ subshell.