Question

to test for amylase, this indicator solution needs to be spread on the surface of the media after incubation:
iodine
starch
acetone - alcohol
zephiran chloride

Explanation:

Amylase is an enzyme that breaks down starch. Iodine reacts with starch to produce a blue - black color. If amylase is present, it will hydrolyze the starch, and when iodine is added, the area where amylase has acted will not turn blue - black (due to the absence of starch), while areas with unhydrolyzed starch will turn blue - black. Starch is the substrate for amylase, not an indicator. Acetone - alcohol is often used as a solvent or in some staining - related wash steps (not for amylase testing). Zephiran chloride is a disinfectant and has no role in amylase - starch - iodine based amylase detection.

Answer:

Iodine