## Core Concept
In this scenario, the 23-year-old woman has been started on Category-I Directly Observed Treatment, Short-Course (DOTS) for tuberculosis (TB), which typically involves a combination of isoniazid, rifampicin, pyrazinamide, and ethambutol. The focus here is on preventing TB in the 2-year-old child, who is asymptomatic and exposed to a potentially infectious TB case.

## Why the Correct Answer is Right
The correct approach for chemoprophylaxis in an asymptomatic child exposed to TB, especially in a setting where the Mantoux test (tuberculin skin test) is not available, is to use Isoniazid Preventive Therapy (IPT). IPT with isoniazid is recommended for children exposed to TB, particularly in high-risk settings or when the child is too young for accurate tuberculin skin testing. This approach helps prevent the progression from latent TB infection to active TB disease.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is blank and cannot be evaluated.
- **Option B:** This option is also blank and cannot be evaluated.
- **Option C:** This option suggests no chemoprophylaxis, which is incorrect because chemoprophylaxis is indicated in a child exposed to an active TB case, especially in a high-risk setting like a remote tribal area with potentially limited access to healthcare.
- **Option D:** This option is blank and cannot be evaluated.

## Clinical Pearl / High-Yield Fact
A key point to remember is that Isoniazid Preventive Therapy (IPT) is a crucial strategy for preventing TB in children exposed to active TB cases, particularly in resource-limited settings where the risk of transmission is high. IPT is especially important for children under 5 years old, as they are at higher risk of developing severe forms of TB.

## Correct Answer Line
**Correct Answer: B. Isoniazid.**