Which of the following statements are correct regarding `Na^+ - K^+` pump ?
(i)Needs energy (ATP) to work
(ii)Expels 3 `Na^+` for every `2K^+` ions imported
(iii)Works against a concentration gradient
(iv)Maintains resting potential

Options

A. (i) and (iv)
B. (ii) and (iii)
C. (i) and (iii)
D. all of these

Explanation

To determine which statements regarding the sodium-potassium (Na⁺-K⁺) pump are correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement (i): Needs energy (ATP) to work**
- The sodium-potassium pump is an active transport mechanism, which means it requires energy to function. This energy is provided by ATP (adenosine triphosphate). Therefore, this statement is **correct**.

2. **Statement (ii): Expels 3 Na⁺ for every 2 K⁺ ions imported**
- The sodium-potassium pump operates by transporting three sodium ions (Na⁺) out of the cell and two potassium ions (K⁺) into the cell. This is a fundamental characteristic of the pump. Thus, this statement is also **correct**.

3. **Statement (iii): Works against a concentration gradient**
- The sodium-potassium pump moves ions against their concentration gradients; sodium ions are moved from an area of lower concentration inside the cell to an area of higher concentration outside, and potassium ions are moved from an area of lower concentration outside the cell to an area of higher concentration inside. Therefore, this statement is **correct**.

4. **Statement (iv): Maintains resting potential**
- The sodium-potassium pump plays a crucial role in maintaining the resting membrane potential of cells. By continuously pumping out Na⁺ and bringing in K⁺, it helps establish the electrochemical gradient necessary for the resting potential. Hence, this statement is **correct**.

### Conclusion:
All four statements about the sodium-potassium pump are correct. Therefore, the correct answer is that all statements are true.