**Core Concept**
The question is testing the understanding of the population coverage of Primary Health Centres (PHCs) in tribal areas. In tribal areas, PHCs are expected to cover a larger population due to the dispersed and scattered nature of the population.

**Why the Correct Answer is Right**
In tribal areas, the population covered by a PHC is 30,000. This is in contrast to the general population coverage of 20,000 for a PHC in a non-tribal area. This increased coverage is necessary to ensure that the remote and inaccessible population in tribal areas has access to basic healthcare services. The increased population coverage is a policy decision aimed at addressing the unique healthcare needs of tribal populations.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not reflect the increased population coverage of PHCs in tribal areas.
* **Option B:** This option is incorrect because it is not specific to tribal areas and does not take into account the unique healthcare needs of tribal populations.
* **Option C:** This option is incorrect because it is not the correct population coverage for PHCs in tribal areas.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that PHCs in tribal areas have a larger population coverage to ensure that the remote and dispersed population has access to basic healthcare services.

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