CBSE Class 10 Science 2018 · Paper 31/1 · Question 22

Colour change is observed in test tubes A, B and D (no change in C). A: the pale green iron sulphate solution becomes colourless, as aluminium displaces iron. B: the blue copper sulphate solution becomes colourless, as aluminium displaces copper. D: the blue copper sulphate solution turns pale green, as iron displaces copper. Aluminium is the most reactive metal, because it displaces both iron and copper from their salt solutions, whereas iron cannot displace aluminium from aluminium sulphate (tube C). Order of reactivity: $\text{Al}>\text{Fe}>\text{Cu}$.