RRB Group D 27 Nov 2025 Shift 2 Solved Paper

Concept:Concentrated sulphuric acid acts as a dehydrating agent because it removes water molecules from certain compounds.Explanation:Glucose is a carbohydrate with the formula $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$.It contains hydrogen and oxygen in the same $2:1$ ratio as water ($\mathrm{H}_2\mathrm{O}$).When treated with concentrated $\mathrm{H}_2\mathrm{SO}_4$, glucose undergoes dehydration to form black carbon and water.The reaction is: $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 \rightarrow 6\mathrm{C} + 6\mathrm{H}_2\mathrm{O}$.The acid absorbs the water produced, clearly showing its dehydrating property.Propane ($\mathrm{C}_3\mathrm{H}_8$) is a hydrocarbon with no water molecules in its structure, so $\mathrm{H}_2\mathrm{SO}_4$ cannot remove water from it.Sodium hydroxide ($\mathrm{NaOH}$) and ammonia ($\mathrm{NH}_3$) also do not contain water in a form that $\mathrm{H}_2\mathrm{SO}_4$ can dehydrate.Thus, only glucose fits the description.Answer:B. Glucose