In which of the following solutions, would the colour of pH strip change to dark blue?

Options

A. HCl
B. NaOH
C. Lemon juice
D. Ethanoic acid

Explanation

To determine in which of the following solutions the color of a pH strip would change to dark blue, follow these steps:

### Step-by-Step Solution:

1. **Understand pH Strips**: pH strips, or litmus paper, are used to determine whether a solution is acidic or basic. Blue litmus paper turns red in acidic solutions, while red litmus paper turns blue in basic solutions.

2. **Identify the Color Change**: The question specifically asks for a solution that causes a pH strip to change to dark blue. This indicates that the solution must be basic (alkaline).

3. **Consider the pH Scale**: The pH scale ranges from 0 to 14. A pH of 7 is neutral, below 7 indicates acidity, and above 7 indicates basicity. Dark blue indicates a strong basic solution, typically with a pH greater than 9.

4. **Evaluate the Given Solutions**: If you have a list of solutions (not provided in the question), identify which ones are known to be basic. Common basic solutions include sodium hydroxide (NaOH), potassium hydroxide (KOH), and ammonia (NH₃).

5. **Select the Correct Solution**: From the list, choose the solution that is basic and would cause the pH strip to change to dark blue.

### Conclusion:
The solution that causes the pH strip to change to dark blue is a basic solution.