(Valance Bond Theory) Magnetic measurements indicate that $[Co(OH_2)_6]^{2+}$ has 3 unpaired electrons. Therefore, the hybridization of the metal's orbitals in $[Co(OH_2)_6]^{2+}$ is :

Question

$(a)\;sp^3\qquad(b)\;sp^2d\qquad(c)\;dsp^2\qquad(d)\;sp^3d^2$