What does red litmus paper indicate when it shows no color change in a solution?

Red litmus paper is used as an indicator for determining the acidity or alkalinity of a solution. When red litmus paper is placed in an acidic solution, it remains red, indicating that the solution is acidic. In a neutral solution, red litmus paper would show no color change, remaining red. This is because neutral solutions, such as pure water, have a pH of about 7, which does not lead to any change in the color of red litmus paper, confirming the neutrality.

When red litmus paper turns blue, it indicates that the solution is basic or alkaline. Therefore, the absence of a color change when using red litmus paper indicates that the solution is neither acidic nor basic, which aligns with the characteristics of a neutral solution. This is why the correct answer is that red litmus paper remaining red signifies a neutral solution.