**Core Concept**
The question is testing the recommendation for chemoprophylaxis in a child exposed to a sputum-positive tuberculosis (TB) patient. Chemoprophylaxis is the administration of antibiotics to prevent the development of active TB disease in individuals who have been exposed to TB.

**Why the Correct Answer is Right**
In children who have been exposed to a sputum-positive TB patient, chemoprophylaxis is recommended to prevent the development of active TB disease. The recommended chemoprophylaxis for children is isoniazid (INH) for 6-9 months, which has been shown to be effective in preventing the development of active TB disease. INH works by inhibiting the synthesis of mycolic acid, a critical component of the TB bacillus cell wall.

**Why Each Wrong Option is Incorrect**
**Option A:** Rifampicin is an essential component of TB treatment, but it is not typically used as monotherapy for chemoprophylaxis in children.
**Option B:** Ethambutol is used in combination with other antibiotics for TB treatment, but it is not recommended for chemoprophylaxis in children due to its potential toxicity.
**Option C:** Isoniazid (INH) is the correct answer, but the duration of treatment is not specified in this option. The recommended duration of INH chemoprophylaxis in children is 6-9 months.

**Clinical Pearl / High-Yield Fact**
The World Health Organization recommends chemoprophylaxis for children who have been exposed to a sputum-positive TB patient, as it is a cost-effective and effective way to prevent the development of active TB disease.

**Correct Answer: D. Isoniazid (INH) for 6-9 months.**