Can you use onion garlic or lemon to kill the smell of alcohol on your breath?

the direct answer is no...you can use things to mask or cover up the smell of alcohol (gum, mints or I guess garlic) but alcohol is absorbed into the blood. Your lungs absorb oxygen from the air you breath and expels carbon dioxide when you exhale. Likewise the alcohol in your blood does produce a smell of alcohol in the air you exhale. This will continue until your body metabolizes the alcohol in you're blood. So yes you can convert it up but you can't "kill" or eliminate it.