The number of $s{p}^2$ hybrid orbitals in a molecule of benzene is_______.

Given data: It is given to identify the number of $sp^2$ hybrid orbitals in a molecule of benzene. 

Explanation: Benzene has a structural formula of $C_6{H}_6$ and contains 6 carbon atoms and 6 hydrogen atoms. Each of these six carbon atoms has three $s{p}^2$ hybrid orbitals and is now $s{p}^2$ hybridised. Consequently, benzene has 18 hybrid orbitals overall. 

Therefore, the correct option is option D.