Which one of the following is a covalent compound?

Carbon dioxide is classified as a covalent compound because it is formed from the sharing of electrons between carbon and oxygen atoms. In carbon dioxide, one carbon atom is double-bonded to two oxygen atoms, resulting in a linear molecular structure. This sharing of electrons allows both carbon and oxygen to attain stable electron configurations, which is characteristic of covalent bonding.

In terms of the other options, sodium hydroxide is an ionic compound composed of sodium cations and hydroxide anions, where electrons are transferred rather than shared. Stearic acid is a long-chain fatty acid that contains ester and carboxyl functionalities, but it primarily consists of a polar region with ionic properties in the carboxylic group, making it less of a purely covalent compound. Paraffin wax, though it consists of long carbon chains, is a mixture of hydrocarbons that can exhibit both covalent and nonpolar characteristics, primarily being classified within the realm of hydrocarbons rather than clearly as a covalent compound like carbon dioxide.