An octahedral complex is formed when hybrid orbitals or the following type are involved

An octahedral complex is formed by sp3d2 or d2sp3 hybrid orbitals. According to the given question-option (a), sp3 gives a tetrahedral geometry. option (b), dsp2 gives a square planar geometry. option (c), d2sp3 gives an octahedral complex option (d) sp2d2 is not possible as is its formation is not possible. Hence, option (c) is the correct answer.