the bond length of Alkanes when compared to Alkenes is

i) A carbon-carbon single bond (Alkanes $C-C$ ) has an average length of 1.54 Angstroms.

ii) A carbon-carbon double bond (Alkenes$C=C$ ) has an average length of 1.33 Angstroms.

iii) A carbon-carbon triple bond (Alkynes $C\equiv C$ ) has an average length of 1.20 Angstroms.

Alkanes contain all carbon- carbon single bonds whereas alkenes contain at least one double bond.