Answer: 0.05%
Step-by-step explanation:
Californian authorities can arrest a driver under the age of 21 for driving under the influence of Alcohol if his/her BAC is 0.05% or higher. The illegal BAC percentage for a driver over the age of 21 is 0.08%.
But even less blood alcohol concentration is considered illegal. For example, for drivers under the age of 21, a BAC of 0.01% is enough to revoke their right to drive for a period of 1 year.