A kidney stone is
(a) Deposition of sand in kidney
(b) Blockage by fats
(c) Blockage by proteins
(d) A salt such as oxalate crystallized in pelvis

Options

A. Deposition of sand in kidney
B. Blockage by fats
C. Blockage by proteins
D. A salt such as oxalate crystallized in pelvis

Answer

To determine what a kidney stone is, let's analyze the options provided in the question step by step.

### Step 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 may cause significant pain when passing through the urinary tract.

### Step 2: Analyzing the Options
- **Option (a)**: "Deposition of sand in kidney" - This is not accurate as kidney stones are not simply sand; they are solid crystals formed from minerals and salts.

- **Option (b)**: "Blockage by fats" - This is incorrect because kidney stones are not caused by fats blocking the kidneys.

- **Option (c)**: "Blockage by proteins" - This is also incorrect; kidney stones are not caused by protein blockage.

- **Option (d)**: "A salt such as oxalate crystallized in pelvis" - This option is correct. Kidney stones are often made up of crystallized salts, including oxalate, which can form in the pelvis of the kidney.

### Step 3: Conclusion
Based on the analysis, the correct answer is:
**(d) A salt such as oxalate crystallized in pelvis.**

---