Total number of ‘$\sigma$ ’ bonds present in $[{\mathrm{B}}_4{\mathrm{O}}_5{\left(\mathrm{OH}\right)}_4{]}^{2-}$ ion is

The structure of $[{\mathrm{B}}_4{\mathrm{O}}_5{\left(\mathrm{OH}\right)}_4{]}^{2-}$ is given below:

There are 18 sigma bonds in $[{\mathrm{B}}_4{\mathrm{O}}_5{\left(\mathrm{OH}\right)}_4{]}^{2-}$.

Therefore, the correct option is (C).