The correct answer is A. From brown to blue-black.
When iodine solution is placed on a cut surface of a potato tuber, a blue-black color change will be noticed. This is because the iodine reacts with the starch in the potato to form a complex that has a blue-black color.
The other options are incorrect because they do not describe the correct color change that will be observed. Option B is incorrect because the color change is not from brown to orange-red. Option C is incorrect because the color change is not from blue to pink. Option D is incorrect because the color change is not from pink to blue-green.
I hope this helps! Let me know if you have any other questions.