Which one of the following statements in regard to the excretion by the human kidneys is correct?

Options

A. Descending limb of loop of Henle is impermeable to water.
B. Distal convoluted tubule is incapable of reabsorbing `Na^(+)` ions.
C. Nearly 99 per cent of the glomerular filtrate is reabsorbed by the renal tubules.
D. Ascending limb of loop of Henle is impermeable to electrolytes.

Answer

To solve the question regarding which statement about excretion by the human kidneys is correct, we will analyze each of the provided statements step by step.

### Step-by-Step Solution:

1. **Understand the Structure of the Nephron**:
- The nephron is the functional unit of the kidney and consists of several parts: Bowman's capsule, proximal convoluted tubule (PCT), loop of Henle (which includes the descending and ascending limbs), distal convoluted tubule (DCT), and collecting duct.

2. **Evaluate the First Statement**:
- **Statement**: "Descending limb of loop of Henle is impermeable to water."
- **Analysis**: The descending limb of the loop of Henle is actually permeable to water, allowing water to be reabsorbed. Therefore, this statement is **false**.

3. **Evaluate the Second Statement**:
- **Statement**: "DCT is incapable of reabsorbing sodium ions."
- **Analysis**: The distal convoluted tubule (DCT) is capable of reabsorbing sodium ions (Na+), as well as other ions. Hence, this statement is also **false**.

4. **Evaluate the Third Statement**:
- **Statement**: "Nearly 99 percent of glomerular filtrate is reabsorbed by the renal tubules."
- **Analysis**: Approximately 180 liters of filtrate is produced daily, but only about 1 to 2 liters is excreted as urine. This indicates that about 99% of the filtrate is indeed reabsorbed by the renal tubules. Therefore, this statement is **true**.

5. **Evaluate the Fourth Statement**:
- **Statement**: "Ascending limb of loop of Henle is impermeable to electrolytes."
- **Analysis**: The ascending limb of the loop of Henle is permeable to electrolytes, particularly sodium and chloride ions, which are reabsorbed here. Thus, this statement is **false**.

6. **Conclusion**:
- The only correct statement regarding the excretion by human kidneys is the third statement: "Nearly 99 percent of glomerular filtrate is reabsorbed by the renal tubules."

### Final Answer:
The correct statement is: **"Nearly 99 percent of glomerular filtrate is reabsorbed by the renal tubules."**