Final answer:
The legal blood alcohol concentration (BAC) limit if you are 21 years or over is 0.08% in most US states.
Step-by-step explanation:
The legal blood alcohol concentration (BAC) limit if you are 21 years or over is 0.08% in most US states. 0.08% BAC means that there is 0.08 grams of alcohol per 100 milliliters of blood. Higher BAC levels can lead to acute intoxication, unconsciousness, and even death. It is important to remember that alcohol affects individuals differently, so it is always safest to avoid drinking and driving altogether.