In the usual iron-nail displacement experiment, a ______ copper(II) sulphate solution becomes ______ as iron(II) sulphate forms.

Explanation

The initial copper(II) sulphate solution is blue. Iron displaces copper, producing pale-green iron(II) sulphate solution and a reddish-brown copper deposit: Fe + CuSO₄ → FeSO₄ + Cu. The colour change is caused by this displacement reaction, rather than by the atmospheric weathering of metallic copper.