**Core Concept**
Vitamin A prophylaxis is a crucial measure to prevent vitamin A deficiency and its consequences, such as night blindness and xerophthalmia. The recommended dose of vitamin A varies according to age, and it is essential to administer the correct dose to ensure effective prophylaxis.

**Why the Correct Answer is Right**
For children aged 1-5 years, the recommended dose of vitamin A is 100,000 IU. However, for children above 5 years, including adolescents, the recommended dose is higher. The World Health Organization recommends a dose of 200,000 IU for children aged 6-12 years and above, including adolescents. This dose is administered every 4-6 months to maintain adequate vitamin A levels and prevent deficiency.

**Why Each Wrong Option is Incorrect**
* **Option A:** 2000 IU is an extremely low dose and would not provide adequate prophylaxis against vitamin A deficiency.
* **Option B:** 20,000 IU is still below the recommended dose for children above 5 years and would not be sufficient to prevent vitamin A deficiency.
* **Option D:** 100,000 IU is the recommended dose for children aged 1-5 years, but it is too low for adolescents aged 16 years.

**Clinical Pearl / High-Yield Fact**
When administering vitamin A prophylaxis, it is essential to ensure that the dose is correct for the child's age. Incorrect dosing can lead to inadequate prophylaxis or even toxicity, which can be severe. Always consult the latest guidelines and recommendations from reputable sources, such as the World Health Organization.

**Correct Answer:**
✓ Correct Answer: C. 200000 iu