**Core Concept**
The question is testing the knowledge of the recommended population norms for Primary Health Centres (PHCs) in tribal areas. In tribal areas, the population norms are different from those in non-tribal areas due to the unique geographical and socio-economic challenges. The recommended population norms for PHCs in tribal areas are designed to ensure that healthcare services are accessible and effective in these areas.

**Why the Correct Answer is Right**
The correct answer is 30,000. This is based on the recommendation of the Ministry of Health and Family Welfare, Government of India, which states that each PHC should cater to a population of 30,000 in tribal areas. This is higher than the recommended population norm of 20,000 for non-tribal areas. This is because tribal areas often have limited access to healthcare services, and a higher population norm is needed to ensure that healthcare services are accessible and effective.

**Why Each Wrong Option is Incorrect**
**Option A:** 20,000 - This is the recommended population norm for non-tribal areas, not tribal areas.
**Option B:** 40,000 - This is higher than the recommended population norm for tribal areas.
**Option C:** 50,000 - This is significantly higher than the recommended population norm for tribal areas.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the population norms for PHCs are not rigid and can be adjusted based on the specific needs of the area. However, in general, tribal areas require a higher population norm to ensure that healthcare services are accessible and effective.

**Correct Answer: D. 30,000**