**Core Concept**
Vitamin A is an essential nutrient, crucial for growth, development, and maintaining healthy vision, immune function, and skin health. In pediatric patients, Vitamin A supplementation is vital for preventing and treating deficiencies, which can lead to conditions like night blindness, impaired immune function, and increased mortality.

**Why the Correct Answer is Right**
For children between 1-3 years, the recommended dose of Vitamin A is 200,000 IU (International Units) every 4-6 months, as per the World Health Organization (WHO) guidelines. This dosage is crucial for maintaining adequate Vitamin A levels and preventing deficiency. The Vitamin A supplementation program aims to provide a single high-dose supplement to children in this age group, which is essential for their growth and development.

**Why Each Wrong Option is Incorrect**
**Option A:** 5,00,000 IU is an excessive dose for children in this age group and can lead to adverse effects like headaches, dizziness, and even liver damage.

**Option C:** 1,00,000 IU is lower than the recommended dose and may not be sufficient to prevent Vitamin A deficiency in children between 1-3 years.

**Option D:** 3,00,000 IU is higher than the recommended dose and can also lead to adverse effects, making it an incorrect choice.

**Clinical Pearl / High-Yield Fact**
It's essential to note that Vitamin A supplementation should only be administered under the guidance of a healthcare professional, and the dosage should be tailored according to the child's age, weight, and nutritional status.

**✓ Correct Answer: B. 2,00,000 IU**