The characteristic odor of garlic is due to the presence of sulphur-containing compounds. Garlic contains a compound called allicin, which is the main contributor to its distinctive smell. Allicin is formed when the enzyme alliinase reacts with the amino acid alliin, both of which are present in garlic. Allicin has a pungent sulfurous smell, which is responsible for the strong aroma that garlic is known for.

Option 1: Chlorine-containing compounds do not contribute to the odor of garlic. Chlorine compounds typically have a different smell, and are not found in garlic.

Option 2: Fluorine-containing compounds also do not contribute to the odor of garlic. Fluorine compounds have a distinct smell and are not present in garlic.

Option 3: Nitrogen-containing compounds are not responsible for the odor of garlic. While nitrogen compounds can have a smell of their own, they are not the primary cause of garlic`s unique aroma.

Therefore, the correct answer is option 4, as sulphur-containing compounds are responsible for the characteristic odor of garlic.