## **Core Concept**
The question pertains to the infrastructure planning of Primary Health Centres (PHCs) in different geographical regions, specifically focusing on hilly or difficult areas. PHCs are integral to the healthcare delivery system in many countries, serving as the first point of contact between the community and the healthcare system.

## **Why the Correct Answer is Right**
In hilly or difficult areas, the population density is often lower, and accessibility to healthcare services can be significantly hampered by geographical barriers. Given these challenges, the healthcare infrastructure needs to be more dispersed to ensure equitable access to healthcare services. The World Health Organization and various national health policies recommend that in hilly, tribal, or difficult areas, one PHC should be present for every 30,000 population, as opposed to plain areas where the norm can be one PHC for 40,000 population. This adjustment accounts for the increased difficulty in accessing healthcare services in these regions.

## **Why Each Wrong Option is Incorrect**
- **Option A:** 40,000 population - This is the norm for plain areas, not hilly or difficult areas.
- **Option B:** 20,000 population - While more accessible PHCs might be beneficial, the specified norm for hilly areas is not this.
- **Option D:** 50,000 population - This would be less than the recommended density for even plain areas, let alone hilly or difficult ones.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the distribution and density of PHCs are adjusted based on the terrain and the population's accessibility to healthcare services. For hilly or difficult areas, the recommended norm is one PHC for every 30,000 population, highlighting the need for increased healthcare infrastructure in these regions to ensure equitable access.

## **Correct Answer:** B. 30,000 population.