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