Copy and complete the following paragraph using the options given in brackets :
Alkenes are a homologous series of (i)........... (saturated / unsaturated) hydrocarbons characterized by the general formula (ii) .......... $\left({\mathrm{C}}_{\mathit{n}}{\mathrm{H}}_{2\mathit{n}+2}∕{\mathrm{C}}_{\mathit{n}}{\mathrm{H}}_{2\mathit{n}}\right)$ . Alkenes undergo (iii).......... (addition / substitution) reactions and also undergo (iv) ......... (hydrogenation / dehydrogenation) to form alkanes.