Final answer:
The blood-alcohol concentration limit for drivers under age 21 in most states is .00 to .02 percent, following a zero-tolerance policy for underage drinking and driving.
Step-by-step explanation:
Most states have a blood-alcohol concentration (BAC) limit of .00 to .02 percent for drivers under age 21. This limit is much lower than the standard .08 percent for drivers over 21, reflecting a zero-tolerance policy for underage drinking and driving. This strict policy is influenced by federal laws such as the National Minimum Drinking Age Act of 1984, which mandates states to set the drinking age at 21 and influences various BAC limits. The intent behind such policies is to discourage any consumption of alcohol by those under 21 and to minimize the risks associated with underage drinking and driving.