A kidney stone is

Options

A. Deposition of sand particles
B. Precipitation of proteins
C. Crystallisation of oxalates
D. Blockage of fat

Answer

**Step-by-Step Solution:**

1. **Understanding Kidney Stones**: Kidney stones are hard deposits made of minerals and salts that form inside the kidneys. They can vary in size and can cause significant pain.

2. **Identifying the Composition**: The most common types of kidney stones are composed of calcium oxalate, calcium phosphate, and uric acid. These substances can crystallize and stick together, forming stones.

3. **Analyzing the Options**:
- **Deposition of sand particles**: This option suggests that kidney stones are formed from small particles, which is somewhat accurate since they can form from crystallized substances.
- **Precipitation of proteins**: This is incorrect as kidney stones are not primarily made of proteins.
- **Crystallization of oxalates**: This option is partially correct because calcium oxalate is a common component of kidney stones.
- **Blockage of fat**: This is incorrect as kidney stones are not related to fat blockage.

4. **Selecting the Correct Answer**: The most accurate option is "crystallization of oxalates," as it directly relates to the formation of kidney stones from calcium oxalate and uric acid.

5. **Conclusion**: Therefore, the correct answer to the question "A kidney stone is" is "crystallization of oxalates."