**Core Concept**
An urban health center is a type of primary health care facility that caters to the specific health needs of urban populations. Urban health centers are designed to provide comprehensive health services to the residents of urban areas, including preventive, promotive, curative, and rehabilitative care.

**Why the Correct Answer is Right**
The correct answer is based on the definition of an urban health center, which is a facility that caters to the urban population. Urban health centers are typically located in densely populated urban areas and provide services such as immunization, family planning, and maternal and child health services. They also provide diagnostic and treatment services for common urban health problems such as respiratory infections and mental health disorders.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because a subcenter is a type of primary health care facility that caters to a population of 5,000 in rural areas, not urban areas.
* **Option B:** This option is incorrect because a community health center is a type of primary health care facility that caters to a population of 80,000 in rural and urban areas, but it is not specific to urban areas.
* **Option C:** This option is incorrect because a block is a subunit of a community development block, which is a geographic area used for administrative purposes, but it is not a type of health care facility.

**Clinical Pearl / High-Yield Fact**
Urban health centers play a critical role in providing accessible and affordable health care services to urban populations, particularly those living in slums and other marginalized areas.

**Correct Answer: D. Urban population.**