$(a)$ What are hydrocarbons?
$(b)$ Write the structural difference between saturated and unsaturated hydrocarbons.

(N/A) Hydrocarbons are organic compounds consisting entirely of carbon and hydrogen atoms linked by covalent bonds.
$(b)$ The structural difference is that saturated hydrocarbons contain only single covalent bonds between carbon atoms (e.g.,alkanes),whereas unsaturated hydrocarbons contain at least one double or triple covalent bond between carbon atoms (e.g.,alkenes or alkynes).