Answer:
4
Step-by-step explanation:
Carbon has 4 electrons in its outer shell that it can share with other atoms. Carbon's favorite partner seems to be hydrogen. Hydrogen's single electron shares space with carbon's outer shell electron and a covalent single bond is formed. C-H is how it's usually shown. Carbon's other three outer shell electrons also want partnerships. A popular compound is methane, CH4. Four hydrogens bond with one carbon atom. These are fairly high energy bonds, as can be demonstrated when methane is combusted in air.
Carbon can also bond to a myriad of other atoms. The compounds that n[make up the human body contain complex carbon-based molecules consisting carbon, hydrogen, oxygen, nitrogen, sulfur, and many others. In all cases, carbon only forms 4 bonds. Some of them may be double bonds, such as the carboxylic acid group -C=O with an -OH group coming off the carbon. That gives it 4 bonds: 2 from the =O, one with the -OH, and one connecting it the the rest of the molecule on the left.