Final answer:
Hydrogen and carbon react to form methane, a compound with the chemical formula CH4, which reflects that carbon has formed four single bonds to satisfy its four valencies with hydrogen atoms.
Step-by-step explanation:
When hydrogen and carbon react, they form methane, which has the chemical formula CH4. Methane is made up of one carbon atom that forms four single bonds with four hydrogen atoms. This is consistent with the requirement that carbon forms four bonds to satisfy its valency and hydrogen forms one bond. The reaction between hydrogen and carbon can be observed in processes such as natural gas formation and organic chemical synthesis.