Final answer:
Carbon's unique properties include its ability to form stable covalent bonds, its tetravalent nature, and its role in diverse and complex molecules.
Step-by-step explanation:
Carbon is unique among the other elements in that its atoms can form stable covalent bonds with each other and with atoms of other elements. Carbon atoms can make a large number of covalent bonds, typically four, due to its four valence electrons. This property allows carbon to form diverse and complex molecules, ranging from small hydrocarbons to large biomolecules, which play a central role in the forms and functions of living systems.