**Core Concept**
The Motor Vehicle Act 1988 in India outlines specific blood alcohol concentration (BAC) limits to determine driving under the influence (DUI). This concept is crucial for medical professionals, as it involves understanding the pharmacokinetics of alcohol, its effects on the central nervous system, and the correlation between BAC and impaired driving.

**Why the Correct Answer is Right**
The correct answer is based on the legal limit set by the Motor Vehicle Act 1988, which is 30 milligrams of alcohol per 100 milliliters of blood (mg/100ml). This limit is established to minimize the risk of accidents caused by impaired driving due to alcohol consumption. The actuarial evidence suggests that drivers with a BAC above this limit are more likely to be involved in accidents.

**Why Each Wrong Option is Incorrect**
**Option A:** 20 mg/100ml - This is below the legal limit and would not be considered punishable under the Motor Vehicle Act 1988.
**Option B:** 40 mg/100ml - This is above the legal limit and would be considered punishable, but it is not the correct answer.
**Option C:** 50 mg/100ml - This is also above the legal limit and would be considered punishable, but it is not the correct answer.

**Clinical Pearl / High-Yield Fact**
It's essential for medical professionals to remember that the Motor Vehicle Act 1988 sets a specific BAC limit, and drivers with a BAC above this limit can be charged with DUI. This knowledge is crucial for accurate diagnosis, treatment, and reporting of cases related to driving under the influence.

**Correct Answer:** 30 mg/100ml