Selective permeability and iodine-starch reaction

Steps:

• Visking tubing allows small molecules like iodine to diffuse through but blocks large molecules like starch.
• After 30 minutes, blue-black color inside the bag indicates starch reacting with iodine, so starch must be in Y and iodine diffuses from X.
• Orange color in the beaker suggests iodine solution (often orange-brown) remaining after diffusion, confirming X contains iodine.
• No enzyme activity implied, as colors result from diffusion and reaction alone.

Why D is correct:

• Visking tubing's semi-permeable nature permits iodine (small molecule) to enter the bag and form blue-black complex with starch, per diffusion principles.

Why the others are wrong:

• A: Amylase would digest starch to maltose (no blue-black); iodine in Y can't explain orange beaker.
• B: Amylase in X digests starch before iodine diffusion; no blue-black forms inside.
• C: Iodine in Y can't diffuse out to orange the beaker; starch in X stays, no blue-black inside.

Final answer: D