The characteristic odour of garlic is due to

The characteristic odour of garlic is produced by volatile organic sulfur-containing compounds formed when garlic tissues are damaged. Enzymatic action (alliinase) on precursors such as alliin yields sulfenic acids that rapidly condense to give the thiosulfinate allicin; allicin and its breakdown products (e.g., diallyl sulfide, diallyl disulfide, diallyl trisulfide and related volatile organosulfur species) are the primary pungent odourants of crushed garlic [2]. Reviews and mechanistic studies explicitly identify allicin-derived volatile sulfur compounds as responsible for the fresh-garlic aroma and for odorous breath metabolites after ingestion [3]. Hence the correct answer is a sulphur compound.

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC8001868/
2. [2] https://lpi.oregonstate.edu/mic/food-beverages/garlic
3. [3] https://pmc.ncbi.nlm.nih.gov/articles/PMC6271412/