(i) Homologous series: A homologous series is a series of organic compounds with similar chemical properties and a gradual change in physical properties, where each member differs by a -CH₂ group. Examples include alkanes, alkenes, and alkynes.
(ii) Versatile nature of Carbon: Carbon is versatile because it can form long chains, rings, and networks, which are the basis for organic chemistry. Carbon atoms can bond with other elements to form a variety of organic compounds, including hydrocarbons, sugars, and proteins.