Solutions in test tubes containing H20 and aqueous NaOH can be differentiated with the help of:

To differentiate between water (H2O) and aqueous sodium hydroxide (NaOH), red litmus paper is the most effective tool. Water is a neutral substance and does not change the color of litmus paper [t2]. In contrast, sodium hydroxide is a strong base [c1]. Basic solutions possess the characteristic property of turning red litmus paper blue [t1][t6]. Blue litmus would not be useful here because it remains blue in both neutral (water) and basic (NaOH) environments, failing to provide a visible distinction [t2]. Similarly, Na2CO3 is a basic salt and does not react visibly with NaOH, and aqueous HCl would undergo a neutralization reaction with NaOH but without a visible indicator, the reaction (forming NaCl and H2O) would not be easily distinguishable from mixing HCl with water unless temperature changes or indicators are monitored [t4][t5].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Activity 2.1 > p. 18