The solution will experience an instant colour change because thiosulphate which is meant to be used as a clocking or Redox reagent which would have to react with iodine is absent.
Step-by-step explanation:
Thiosulphate is a chemical reagent that is used in chemical reactions such as titrations.
Thiosulphate is used as in the chemical reaction called Iodometry. This is a reaction whereby Thiosulphate is used as reactant and it is titrated against iodine in order to obtain an endpoint.
If Thiosulphate is not added to the test tube, there would be a colour change that occurs instantly because Thiosulphate did not react with iodine.
