Answer
a) Alkanes have the general formula $C_{n}H_{2n+2}$
whereas Alkenes have the general formula $C_{n}H_{2n}$
b) Alkenes & Cycloalkanes have the same general formula $C_{n}H_{2n}$. This is because in Cycloalkanes, Carbon atoms bond together to form a ring and there is no terminal Carbon. Due to formation of ring, every C atom must have to saturated with 2 Hydrogen atoms (see below example). So, for 'n' no. of C atoms there should be '2n' no. of H atoms. So, the formula is $C_{n}H_{2n}$ which is identical with the general formula for Alkenes.
Work Step by Step
a) Alkanes have the general formula $C_{n}H_{2n+2}$
whereas Alkenes have the general formula $C_{n}H_{2n}$. This is because in Alkenes there is double bond between two Carbon atoms i.e. all 'C' atoms are not completely saturated with H atoms (Carbons attached with double bond are bonded with 3 atoms. That's why the C is unsaturated) Where as in Alkanes all 'C' atoms are completely saturated with H atoms (Here, every C atoms are bonded with 4 atoms. That means complete saturation occur for every C atom) as there is only C-C single bond present in alkanes.
b) See the answer with explanation.
