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) .......... (CnH2n+2∕CnH2n) . Alkenes undergo (iii).......... (addition / substitution) reactions and also undergo (iv) ......... (hydrogenation / dehydrogenation) to form alkanes.