Bases turn red litmus blue and acids turn blue litmus red. A student tested a liquid with a red litmus paper and it stayed red with no change. This shows that the liquid

Bases are substances that change the color of red litmus paper to blue [c1][c2]. If a liquid is tested with red litmus paper and it stays red with no change, it indicates that the liquid is not a base [t3][t7]. Red litmus paper remains red in both acidic and neutral solutions [t2][t8]. Therefore, while the liquid could be an acid (which turns blue litmus red but leaves red litmus unchanged) or a neutral substance like pure water, the only definitive conclusion that can be drawn from the red litmus paper remaining red is that the substance is not basic [t3][t8]. Option 1 and 2 are incorrect because the liquid could be either an acid or neutral; option 4 is incorrect because the liquid could be an acid. Thus, the most accurate deduction 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
2. [2] Science-Class VII . NCERT(Revised ed 2025) > Chapter 2: Exploring Substances: Acidic, Basic, and Neutral > 2.3 Neutralisation in Daily Life > p. 19