Which of the following describes a primary carbon?

A primary carbon is defined as a carbon atom that is bonded to only one other carbon atom. It typically appears at the end of a carbon chain, making it terminal in that sense. This structure is commonly observed in alkane chains, where the primary carbon is at one end of the molecule.

Primarily, this designation helps in understanding the reactivity and properties of the molecule, especially in organic chemistry, where the position of carbon atoms and their bonding influence the behavior of the compounds in reactions.

In contrast, a carbon bonded to three other carbons (the first choice) would be classified as a tertiary carbon, while a carbon bonded to no other carbons would be a carbon atom that is part of a functional group, like a methyl (-CH3) group, which is also not considered primary in this context. A carbon bonded to one other carbon (the second choice) would usually be part of a functional group but is not a terminal carbon unless specified. Thus, the terminal nature of the primary carbon makes it correctly categorized under this designation.