Fehling's solution 'A' is:

Solution & Explanation

\textbf{Answer:} (D) aqueous copper sulphate \textbf{Solution:} Fehling's reagent is prepared from two solutions mixed just before use: Fehling's solution 'A' is aqueous copper sulphate $\mathrm{CuSO}{}_4$, and Fehling's solution 'B' is an alkaline solution of sodium potassium tartrate (Rochelle's salt). The reagent detects aliphatic aldehydes, which reduce $\mathrm{Cu}{}^{2+}$ to a red-brown precipitate of $\mathrm{Cu}{}_2\mathrm{O}$.