Final answer:
A person with 50 mg of alcohol per 100 mL of blood has a BAC of 0.05, which is calculated by dividing the mass of alcohol by the blood volume and converting to a percentage.
Step-by-step explanation:
A person with 50 mg of alcohol per 100 mL of blood would have a blood alcohol concentration (BAC) of 0.05. This is calculated by taking the mass of alcohol and dividing it by the total volume of blood, and then converting this ratio into a percentage. Since there are 50 mg of alcohol per 100 mL of blood, the BAC is 50 mg/dL, which, when converted into the percentage form, is 0.05%. This level of BAC is significant and in many jurisdictions, would be at or above the legal limit for driving.