**Core Concept**
Microcalcifications are small calcium deposits found in breast tissue, visible on mammography. They are a common finding and can be associated with benign or malignant conditions. The size and distribution of microcalcifications are crucial in differentiating between these two possibilities.

**Why the Correct Answer is Right**
The American College of Radiology (ACR) and the Breast Imaging-Reporting and Data System (BI-RADS) define microcalcifications as small, discrete calcifications measuring less than **1 mm** in diameter. This size threshold is essential in distinguishing microcalcifications from larger calcifications, which may be associated with benign conditions like fibroadenomas or vascular calcifications.

**Why Each Wrong Option is Incorrect**
**Option A:** **2 mm** is too large to be considered a microcalcification, as it may represent a larger calcification or a cluster of smaller ones.
**Option B:** **0.5 mm** is a reasonable size for a microcalcification, but the correct answer is smaller.
**Option C:** **5 mm** is significantly larger than a microcalcification and would be considered a macrocalcification.

**Clinical Pearl / High-Yield Fact**
When interpreting mammography, it's essential to remember that the size, distribution, and morphology of microcalcifications are critical in differentiating between benign and malignant conditions. A cluster of microcalcifications with irregular shapes or linear or segmental distributions may be highly suggestive of malignancy.

**Correct Answer:** C. 5 mm