Which of the following statements is correct about an aqueous solution of an acid and a base?
(i) higher the pH stronger the acid
(ii) Higher the pH, weaker the acid
(iii) Lower the pH, stronger the base
(iv) Lower the pH, weaker the base

Options

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

Explanation

To determine which statement is correct about an aqueous solution of an acid and a base, we need to understand the relationship between pH, acids, and bases.

### Step-by-Step Solution:

1. **Understanding pH**:
- pH is a measure of the hydrogen ion concentration \([H^+]\) in a solution. It is calculated using the formula:
\[ pH = -\log[H^+] \]
- A lower pH value indicates a higher concentration of hydrogen ions, which means a stronger acid.

2. **Analyzing the Statements**:
- **Statement (i)**: "Higher the pH stronger the acid."
- This statement is incorrect. A higher pH indicates a lower concentration of hydrogen ions, which means the acid is weaker.

- **Statement (ii)**: "Higher the pH, weaker the acid."
- This statement is correct. As pH increases, the acidity decreases, indicating a weaker acid.

- **Statement (iii)**: "Lower the pH, stronger the base."
- This statement is incorrect. A lower pH indicates a stronger acid, not a stronger base.

- **Statement (iv)**: "Lower the pH, weaker the base."
- This statement is correct. A lower pH indicates a stronger acid and thus a weaker base.

3. **Conclusion**:
- The correct statements about an aqueous solution of an acid and a base are:
- (ii) Higher the pH, weaker the acid.
- (iv) Lower the pH, weaker the base.

### Final Answer:
The correct statements are (ii) and (iv).