Which of the following best describes how a trihalomethane molecule differs from a methane molecule?

• A. A trihalomethane contains three carbon atoms instead of one.
• B. In a trihalomethane, three hydrogen atoms in ${\mathrm{CH}}_4$ are replaced by halogen atoms.
• C. A trihalomethane has all four hydrogens replaced by halogen atoms.
• D. A trihalomethane has an oxygen atom double-bonded to the carbon.

Answer: (B)

Verified step by step guidance

1. Recall the structure of methane, which is represented as \(\mathrm{CH_4}\), consisting of one carbon atom bonded to four hydrogen atoms.
2. Understand that a trihalomethane is a derivative of methane where three of the hydrogen atoms are replaced by halogen atoms (such as fluorine, chlorine, bromine, or iodine).
3. Recognize that the term 'trihalomethane' specifically means 'three halogen atoms attached to methane,' so the carbon count remains the same (one carbon atom).
4. Compare the options given: the correct description should mention the replacement of exactly three hydrogen atoms by halogen atoms, not all four or a change in the number of carbon atoms.
5. Conclude that the best description is that in a trihalomethane, three hydrogen atoms in \(\mathrm{CH_4}\) are replaced by halogen atoms, maintaining the single carbon atom structure.