The correct answer is A. acetic acid.
Acetic acid is a polar molecule, which means that it has a positive end and a negative end. This polarity allows the molecules of acetic acid to form hydrogen bonds with each other. Hydrogen bonds are strong intermolecular forces that hold molecules together. The stronger the intermolecular forces, the higher the boiling point of the substance.
Chloroform, ethanol, and methane are all nonpolar molecules. Nonpolar molecules do not have a positive end or a negative end, so they cannot form hydrogen bonds. The lack of hydrogen bonds in these molecules results in lower boiling points.
Acetic acid has a boiling point of 118 degrees Celsius. Chloroform has a boiling point of 61 degrees Celsius. Ethanol has a boiling point of 78 degrees Celsius. Methane has a boiling point of -161 degrees Celsius.
Therefore, acetic acid has the highest boiling point of the four substances.