On adding a clean Aluminium strip to an aqueous solution of copper sulphate, it is observed that the colour of the solution changes from .

According to the Reactivity Series (Table 3.2), Aluminium ($Al$) is more reactive than Copper ($Cu$). When an Aluminium strip is added to a blue-coloured aqueous solution of copper sulphate ($CuSO_4$), a displacement reaction occurs as described in Section 3.2.4. Aluminium displaces copper to form aluminium sulphate ($Al_2(SO_4)_3$), which is a colourless solution, and reddish-brown copper metal is deposited. The reaction is: $2Al(s) + 3CuSO_4(aq) \rightarrow Al_2(SO_4)_3(aq) + 3Cu(s)$. Therefore, the blue colour of the solution fades and eventually becomes colourless. Option B is incorrect as it suggests the reverse. Option C and D are incorrect because green colour is associated with iron(II) sulphate, not aluminium sulphate.