Given below from (i) to (iv) are some food items.

(i) Boiled and mashed potato

(ii) Glucose solution

(iii) A slice of bread

(iv) Mustard oil

Which of the above will give blue-black colour when tested with iodine?

Starch gives blue black colour when tested with iodine. Among the given options, boiled & mashed potato and bread slice will have starch in them therefore, they will give blue black colour with iodine.

While mustard oil and glucose solution doesn't not have starch content in them. They have fats and glucose content respectively.