RRB Group D 27 Nov 2025 Shift 1 Solved Paper

Concept:Zinc is more reactive than copper. It displaces copper from copper sulphate solution. This is a displacement reaction.Explanation:When a zinc rod is placed in aqueous copper sulphate ($\mathrm{CuSO}_4$) solution, zinc (Zn) replaces copper (Cu) because zinc is higher in the reactivity series.The reaction is: $\mathrm{Zn} + \mathrm{CuSO}_4 \rightarrow \mathrm{ZnSO}_4 + \mathrm{Cu}$.Zinc sulphate ($\mathrm{ZnSO}_4$) formed is colourless, while copper sulphate has a blue colour.As the reaction proceeds, the blue colour fades due to the disappearance of $\mathrm{Cu}^{2+}$ ions.Copper metal deposits on the zinc rod as a reddish‑brown layer.This reaction occurs spontaneously without any external heating.It is slightly exothermic, so the temperature does not fall; it may rise slightly.A clear chemical change is observed, so options involving no change, need for heat, or temperature drop are incorrect.Answer:Option A: The blue colour of the copper sulphate solution fades.