Silver articles turn black when they react with sulphur in the air, forming a coating of silver sulphide.

Functional groups are specific arrangements of atoms within a molecule, and they are denoted by their free valency. These groups, containing heteroatoms, confer distinct properties to carbon compounds, independent of the carbon chain’s characteristics.

Elements replacing hydrogen in a hydrocarbon chain are called heteroatoms. These heteroatoms, including halogens, oxygen, nitrogen, and sulphur, form functional groups in compounds, imparting specific properties regardless of the carbon chain’s length and nature.

Carbon forms bonds not only with hydrogen but also with halogens, oxygen, nitrogen, and sulphur. These elements can replace hydrogen in a hydrocarbon chain, maintaining carbon’s valency.

Carbon’s unparalleled catenation is attributed to its capacity to form strong bonds with other carbon atoms. With a valency of four, carbon can bond with multiple atoms, producing stable compounds with diverse elements due to the strength of its bonds.