Question

if you did a biuret test and the sample turned purple, for which of the molecules is the sample positive?

Explanation:

The Biuret test is used to detect proteins. Proteins are polymers of amino - acids linked by peptide bonds. A positive Biuret test (purple color) indicates the presence of a peptide bond - containing molecule. The first option shows a chain of amino - acids linked by peptide bonds, which is a protein.

Answer:

The first option (the chain of amino - acids linked by peptide bonds)