Which of the following statements are correct?
(i). Reabsorption of water occurs passively in the initial segment of nephron.
(ii). Nitrogenous wastes are absorbed by passive transport.
(iii). Conditional reabsorption of `Na^(+)` and water takes palce in DCT.
(iv). DCT reabsorbs `HCO_(3)^(-)`
(v). DCT is capable of selective secretion of `H^(+),K^(+)` and `NH_(3)` to maintain pH and `Na^(+)-K^(+)` balance in blood.
(vi). Substance like glucose, amino acids, `Na^(+)`, etc,. it the filtrate are reabsorbed actively.

Options

A. a)(i) and (ii)
B. b) (ii) and (iii)
C. c) (iv) and (v)
D. d) all of these

Answer

To determine which statements about the nephron and its functions are correct, let's analyze each statement one by one:

### Step-by-Step Solution:

1. **Statement (i)**: "Reabsorption of water occurs passively in the initial segment of nephron."
- The initial segment of the nephron is the Proximal Convoluted Tubule (PCT). Water reabsorption in the PCT occurs passively through osmosis. Therefore, this statement is **correct**.

2. **Statement (ii)**: "Nitrogenous wastes are absorbed by passive transport."
- Nitrogenous wastes such as ammonia, urea, and uric acid are primarily reabsorbed in the PCT, and this process involves passive transport. Thus, this statement is **correct**.

3. **Statement (iii)**: "Conditional reabsorption of `Na^(+)` and water takes place in DCT."
- In the Distal Convoluted Tubule (DCT), sodium ions and water can be reabsorbed conditionally, influenced by hormones such as aldosterone. Therefore, this statement is **correct**.

4. **Statement (iv)**: "DCT reabsorbs `HCO3^(-)`."
- The DCT does indeed reabsorb bicarbonate ions (HCO3^(-)) to help maintain acid-base balance in the body. Thus, this statement is **correct**.

5. **Statement (v)**: "DCT is capable of selective secretion of `H^(+)`, `K^(+)`, and `NH3` to maintain pH and `Na^(+) - K^(+)` balance in blood."
- The DCT is involved in the selective secretion of hydrogen ions (H^+), potassium ions (K^+), and ammonia (NH3) to regulate pH and maintain electrolyte balance. Therefore, this statement is **correct**.

6. **Statement (vi)**: "Substances like glucose, amino acids, `Na^(+)`, etc., in the filtrate are reabsorbed actively."
- Glucose, amino acids, and sodium ions are reabsorbed actively in the PCT. Therefore, this statement is **correct**.

### Conclusion:
All the statements (i) to (vi) are correct. Therefore, the correct option is that all of these statements are correct.