## Core Concept
A community development block (CD block) is a rural area earmarked for administration and development in India. It is a cluster of villages or a group of villages with a population that serves as a unit for implementing developmental programs.

## Why the Correct Answer is Right
The correct population covered by a community development block is approximately 60,000 to 120,000 people, but more commonly defined as 100,000. This population range allows for effective administration of health, education, and other developmental programs at the grassroots level.

## Why Each Wrong Option is Incorrect
* **Option A:** 10,000 - This population is too small for a community development block and is more suitable for a sub-center, the most peripheral and first contact point between the primary healthcare system and the community.
* **Option B:** 200,000 - This is larger than the typical population covered by a CD block. While variations exist based on the state and region's needs, 200,000 is generally considered too large for a single block.
* **Option D:** 500,000 - This population size is significantly larger than what a community development block typically covers and might be more aligned with the population served by a district hospital or a larger administrative unit.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the structure of community development blocks and their population coverage can vary slightly by state in India, but generally, a CD block covers around 100,000 population. This structure is crucial for planning and delivering primary healthcare services.

## Correct Answer: C. 100,000.