A drop of a liquid sample was put on the pH paper. It was observed that the colour of the pH paper turned blue. The liquid sample is

1. lemon juice
2. sodium bicarbonate solution
3. distilled water
4. hydrochloric acid

Correct Answer:  (b) sodium bicarbonate solution

Explanation: The liquid sample is of sodium bicarbonate (NaHCO₃) solution. It is a basic solution. And we know that a basic solution turns pH paper blue.