**Core Concept**
The term "Plains" refers to a specific geographic area in India, and the question is asking about the population covered by a female health worker in this region. This concept is related to the health infrastructure and workforce planning in rural areas of India.

**Why the Correct Answer is Right**
In the context of rural health care in India, a female health worker, specifically a Female Multipurpose Health Worker (FMPHW) or an Auxiliary Nurse Midwife (ANM), is responsible for providing primary health care services to a population of approximately 1000 individuals. This includes maternal and child health care, family planning, and basic medical care. The health worker is an essential component of the rural health system, bridging the gap between the community and the health system.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not match the standard population coverage of a female health worker in the Plains region.
**Option B:** This option is incorrect because it exceeds the typical population coverage of a female health worker in the Plains region.
**Option C:** This option is incorrect because it is below the standard population coverage of a female health worker in the Plains region.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the population coverage of a female health worker can vary depending on the region and the specific health infrastructure. However, in general, a female health worker is responsible for providing primary health care services to a population of approximately 1000 individuals.

**Correct Answer: 1000**