The molecular orbital picture of benzene shows that in it all the six carbon atoms are $\mathrm{sp}^{2}$ hybridised. Out of these three ${s p^{2}}^{2}$ hybrid orbitals of each C atom, two orbitals overlap with $\mathrm{sp}^{2}$ hybrid orbitals of adjacent $C$ atoms to form six $\mathrm{C}-\mathrm{C}$ single bonds. The remaining $\mathrm{sp}^{2}$ orbital of each $C$ atom overlaps with -orbital of each hydrogen atom to form six $\mathrm{C}-\mathrm{H}$ single sigma bonds. Each C atom is now left with one unhybridised -orbital perpendicular to the plane of the ring.