Which one of the following tests used for the identification of functional groups in organic compounds does not use copper reagent?

First, let us recall the main reagents that appear in each of the four classical qualitative tests listed in the question.

We know that the presence or absence of copper(II) ions, written chemically as $$Cu^{2+}$$, is decisive here, because the wording asks which test “does not use copper reagent.” So we will look at every test one by one and explicitly state whether copper ions participate in the procedure.

1. Seliwanoff’s test: This test is designed to distinguish ketoses from aldoses. The reagent is an ethanolic solution of resorcinol mixed with concentrated $$HCl$$. The ketose, if present, undergoes rapid dehydration in the strongly acidic medium, forming hydroxymethylfurfural, which then condenses with resorcinol to give a cherry-red complex. There is no mention, requirement, or role of copper ions in this entire sequence.

2. Biuret test: The Biuret reagent contains $$CuSO_{4}$$ in a strongly alkaline solution (usually $$NaOH$$ or $$KOH$$). The peptide bonds in proteins form a violet-coloured coordination complex with $$Cu^{2+}$$. Hence this test unequivocally employs copper ions.

3. Barfoed’s test: Barfoed’s reagent is prepared from $$Cu(CH_{3}COO)2$$ (copper(II) acetate) dissolved in dilute acetic acid. It is used to detect monosaccharides specifically, and the Cu(II) is reduced to Cu(I) oxide, giving a brick-red precipitate. Thus copper ions are essential here as well.

4. Benedict’s test: Benedict’s qualitative reagent contains $$CuSO_{4}$$, sodium citrate, and sodium carbonate. Reducing sugars reduce the blue $$Cu^{2+}$$ to insoluble red $$Cu_{2}O$$. Therefore, copper ions again play the central role.

Looking at all four results together, only Seliwanoff’s test operates without any copper reagent; the other three rely directly on $$Cu^{2+}$$ chemistry.

Hence, the correct answer is Option A.