**Core Concept**
Rubella immunoglobulin is a preparation of antibodies against the rubella virus, used to provide temporary immunity in individuals exposed to the virus or in those with a compromised immune system. The dose of rubella immunoglobulin is crucial in preventing the development of rubella.

**Why the Correct Answer is Right**
The dose of rubella immunoglobulin is typically 400-500 IU/kg body weight, administered within 72 hours of exposure. This dose provides adequate levels of neutralizing antibodies to prevent the establishment of a rubella infection. The immunoglobulin works by binding to and neutralizing the rubella virus, thereby preventing it from infecting host cells.

**Why Each Wrong Option is Incorrect**
**Option A:** 100-200 IU/kg body weight is an incorrect dose, as it may not provide sufficient levels of neutralizing antibodies to prevent the development of rubella.
**Option B:** 1500-2000 IU/kg body weight is an excessive dose, which may lead to adverse reactions without providing additional benefit.
**Option C:** 50-100 IU/kg body weight is an insufficient dose, which may not provide adequate protection against the rubella virus.

**Clinical Pearl / High-Yield Fact**
It is essential to administer rubella immunoglobulin within 72 hours of exposure to the virus, as this is the optimal timeframe for preventing the development of rubella.

**Correct Answer: C. 400-500 IU/kg body weight**