What is the colour of litmus solution when it is neither acidic nor basic?

Purple

The correct answer is option 3. Purple.

Litmus is a natural dye extracted from lichens, and it is commonly used as an acid-base indicator. It changes color in response to changes in the pH of the solution it is added to. Litmus is available in two forms: blue litmus and red litmus.

Blue litmus: Blue litmus paper turns red in acidic solutions and remains blue in neutral or basic solutions.

Red litmus: Red litmus paper turns blue in basic solutions and remains red in neutral or acidic solutions.

When litmus solution is neither acidic nor basic, meaning it is in a neutral state, it appears purple. This is because the litmus solution contains a mixture of both blue and red litmus dyes. In a neutral solution with a pH of around 7, the color change of litmus is balanced between the red and blue forms, resulting in a purple color.

Therefore, purple is the color of litmus solution when it is neither acidic nor basic, indicating a neutral pH.