**Core Concept**
The **Barr body** is a compact, inactivated **X chromosome** found in female mammals, which helps maintain **dosage compensation** between males (XY) and females (XX) for genes located on the X chromosome. This concept is crucial in understanding **genetic** and **cellular biology**. The Barr body is typically visible during interphase.

**Why the Correct Answer is Right**
The Barr body is most easily visible during **interphase**, specifically when the cell is not dividing and the chromatin is less condensed. This allows for the identification of the inactivated X chromosome. The **interphase** stage of the cell cycle is when the cell grows, replicates its DNA, and prepares for cell division, making it the ideal time to observe the Barr body.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the Barr body is not typically associated with the **prophase** stage of mitosis, where chromosomes begin to condense.
**Option B:** This option is also incorrect as the Barr body is not a distinct feature during **metaphase**, where chromosomes line up at the cell's equator.
**Option D:** Similarly, this option is incorrect because the Barr body's presence is not characteristic of the **telophase** stage, where nuclear envelopes reform around each set of chromosomes.

**Clinical Pearl / High-Yield Fact**
Remember, the Barr body is a key concept in **cytogenetics** and understanding **sex chromosome abnormalities**, such as **Turner syndrome** (45,X) and **Klinefelter syndrome** (47,XXY).

**Correct Answer:** D. Interphase.