RRB ALP CBT I 13 Feb 2026 Shift 1 Paper

Concept:A displacement reaction occurs when a more reactive element replaces a less reactive element from its compound.A reaction that shows ion exchange between two compounds is a double displacement reaction, not a simple displacement reaction.Explanation:Consider option A: $\mathrm{Na + H_2O \rightarrow NaOH + H_2}$Here, sodium displaces hydrogen from water, so it is a displacement reaction.Option B: $\mathrm{Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2}$Zinc displaces hydrogen from sulphuric acid, so it is a displacement reaction.Option C: $\mathrm{Fe + CuSO_4 \rightarrow FeSO_4 + Cu}$Iron is more reactive than copper and displaces copper from copper sulphate, so it is a displacement reaction.Option D: $\mathrm{HCl + NaOH \rightarrow NaCl + H_2O}$This is an acid-base neutralisation reaction in which $\mathrm{H^+}$ and $\mathrm{OH^-}$ ions combine to form water.It is a double displacement reaction, not a single displacement reaction.Therefore, the reaction that is NOT a displacement reaction is option D.Answer:D. $\mathrm{HCl + NaOH \rightarrow NaCl + H_2O}$