Acid turns blue litmus red and base turns red litmus blue. A student tested a liquid with a red litmus paper which remained red with no change. This shows that the liquid

Litmus paper is a natural indicator used to distinguish between acidic, basic, and neutral substances. According to the principles of chemistry, bases turn red litmus paper blue [1]. If a student tests a liquid with red litmus paper and it remains red with no change, it indicates that the substance is not a base. This is because red litmus paper stays red in both acidic and neutral environments [1]. For instance, distilled water (neutral) and vinegar (acidic) would both leave red litmus paper unchanged. Therefore, while the liquid could be either an acid or a neutral substance like pure water, the only definitive conclusion that can be drawn from the lack of color change on red litmus paper is that the liquid is not a base.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > p. 17