Question

if you did an iodine test and the sample turned black or dark brown, for which of the molecules is the sample positive?

Explanation:

The iodine - starch test is a well - known biochemical test. Starch is a polysaccharide. When iodine reacts with starch, it forms a blue - black or dark brown complex due to the interaction between iodine molecules and the helical structure of amylose (a component of starch). The first option shows a protein structure (with peptide bonds and amino acids), the second option is a monosaccharide structure, the third option appears to be a lipid structure, and the fourth option is a polysaccharide structure similar to starch.

Answer:

The polysaccharide - like structure (the fourth option)