Prove which test tubes contain solutions of a) sodium chloride and b) sodium hydroxide c) hydrochloric acid

To prove the content of any substance in test tubes, we need to carry out a reaction, but with the condition that this reaction proceeds. That is, in the course of the reaction performed, a precipitate should precipitate, gas should be released or water formed (like a weak electrolyte). If the reaction meets the specified conditions, then we can compare the reaction products. Therefore:

NaCl + AgNO3 = AgCl + HNO3 (AgCl precipitates, this precipitate is white);

2NaOH + ZnSO4 = Na2SO4 + Zn (OH) 2 (Zn (OH) 2 also precipitates, but it looks like colorless crystals);

HCl + KOH = KCl + H2O (a common neutralization reaction, during which water is formed).