The positive control for the iodine test was the
A.
Distilled water
B.
Olive oil
C.
Albumin solution
D.
Starch solution
The positive control for the iodine test is:
D. Starch solution
Explanation:
The iodine test (or iodine-starch test) is used to detect the presence of starch. Iodine reacts with starch to produce a blue-black color. Therefore, a starch solution is used as a positive control because it reliably produces a color change when iodine is added, indicating the presence of starch.
Here’s why the other options are not appropriate as a positive control for this test:
- A. Distilled water: This does not contain starch and would not produce a color change with iodine.
- B. Olive oil: This is a fat and does not contain starch, so it would not give a positive result with iodine.
- C. Albumin solution: This is a protein and does not react with iodine to give a color change, so it is not suitable for this test.
Thus, D. Starch solution is the correct positive control for the iodine test.