Final answer:
A methyl substituent has the molecular formula B. CH3, where it consists of one carbon atom bonded to three hydrogen atoms.
Step-by-step explanation:
The question asks for the molecular formula of a methyl substituent, which is part of organic chemical nomenclature. The correct answer is B. CH3. This is because a methyl group consists of one carbon atom bonded to three hydrogen atoms, thus having the molecular formula CH3. It is a common substituent in organic chemistry and is derived from methane (CH4) where one hydrogen is removed, leaving a methyl group (CH3) that can attach to other carbon atoms in bigger organic molecules such as 2,3-dimethylbutane, where the methyl groups are the substituents.