What name is given to the solutions that don’t affect the colour of either the red or the blue litmus test strips?

Neutral solutions

The correct answer is option 4. Neutral solutions.

Litmus paper is a commonly used indicator to determine the acidity or basicity of a solution. It comes in two colors: red and blue. Red litmus paper turns blue in the presence of a basic solution, while blue litmus paper turns red in the presence of an acidic solution. However, there are substances that do not cause any color change in litmus paper. These substances are associated with neutral solutions.

Neutral solutions are neither acidic nor basic on the pH scale. They have a pH of 7, which is considered neutral. When litmus paper is exposed to a neutral solution, it does not exhibit any color change. The red litmus paper stays red, and the blue litmus paper remains blue.

Water is a common example of a neutral solution. Pure water has a pH of 7 and does not alter the color of litmus paper. Other substances, like certain salts, may also produce a neutral solution when dissolved in water, depending on the nature of the ions involved.

In summary, solutions that don't affect the color of litmus paper are referred to as neutral solutions, having a pH close to 7 on the pH scale.