Revision notes
Alkanes: $\text{C}_n\text{H}_{2n+2}$; alkenes: $\text{C}_n\text{H}_{2n}$; alkynes: $\text{C}_n\text{H}_{2n-2}$. Benzene is $\text{C}_6\text{H}_6$. Butane ($\text{C}_4\text{H}_{10}$) has two structural isomers: n-butane and isobutane.