Move the slider on the burette to the top to add about 25 mL of NaOH to the flask. What happens, and what does this tell you about the pH of the flask

See explanation

Explanation:

An acid is any solution that donates protons while a base is any solution that accepts protons.

A litmus paper can be used to indicate whether a solution is acidic or basic. Litmus paper turns red in an acid solution and blue in a basic solution.

When you move the slider on the burette to the top and add about 25mL of NaOH to the flask, the colour turns blue showing that the solution is now basic.