Padma took a little sodium hydroxide in a beaker and dipped a red litmus paper into it. She observed red litmus paper turned blue. She took dilute hydrochloric acid in the same beaker and dipped a blue litmus paper into it. The blue litmus paper did not turn red. Why ?

Explanation

1. Padma took dilute hydrochloric acid in the same beaker containing sodium hydroxide solution.
2. Mixing of base to acid forms salt, which is a neutral and does not change the colour of either blue or red litmus paper.