(a) Compounds of carbon and hydrogen are called hydrocarbons. Example methane, ethane etc.
(b) Saturated hydrocarbons contain carbon-carbon single bonds, unsaturated hydrocarbon contains at least one carbon-carbon double or triple bond.
(c) Functional group - An atom/group of atoms joined in a specific manner which is responsible for the characteristic chemical properties of the organic compounds. Examples are hydroxyl group (-OH), aldehyde group (-CHO), Carboxylic group (-COOH), ketone group C=O etc.