A 150-pound man and a 200-pound man both consume 4 beers over 1 hour on an empty stomach. Both are 30 years old. Whose Blood Alcohol Content (BAC) will be higher?

For a given amount of alcohol consumed, a person with a lower body weight will have a higher BAC because the alcohol is distributed in a smaller volume of body fluids. Conversely, a person with a higher body weight will have a lower BAC.

We are comparing a 150-pound man to a 200-pound man, both consuming the same amount of alcohol (4 beers) under the same conditions (30 years of age, empty stomach, over 1 hour).

Since the 150-pound man has a lower body weight than the 200-pound man, the alcohol will be less diluted in his body. Therefore, his BAC will be higher.

Comparing this to the given options:
a. The 150-pound man would have a BAC higher than the 200-pound man.
b. The 150-pound man would have a BAC lower than the 200-pound man.

Option a is correct.

The final answer is $\boxed{\text{a. The 150-pound man would have a BAC higher than the 200-pound man.}}$