Alkenes are saturated unreactive single bonds very reactive

            Alkenes are Very Reactive.

Explanation:
                   Other options are incorrect because;

Saturated compounds are those hydrocarbons which contains only single bonds, while alkenes contain atleast one double bond.

Single bonds again stands for saturated compounds, hence it is false.

Alkene are reactive because the double bond has the potential to open by addition reaction. So electrophiles are readily added across double bond. This reactivity can also be explained by the exposure of nucleophilic double bond above and below the plane, which is highly exposed to incoming electrophiles.

The formula is (nh4)2co3