Aresearcher is designing a laboratory experiment to determine whether the inorganic substance a affects the rate of a reaction between two colored liquids, x and y. when the reaction is complete, the liquid is clear. the reaction between x and y is similar to one used by manufacturers to produce certain chemicals in factories. which method would best answer his question about reaction rate and what will he find out about substance a?

Initially he should measure that how much time it takes for the liquid to turn clear if X and Y are mixed together. After that he should find out that how much time it takes if he also supplements substance A to X and Y, to find that whether the substance is a catalyst or not.

Explanation:

Determining the time consumed for the liquid to turn clear when X and Y were combined together will give a prediction about the rate of reaction and the time of reaction.  

The same method should be followed when component A is supplemented to the liquid X and Y mixture. If a fast reaction takes place with the supplementation of A to the reaction mixture then it can be said that A functions as a catalyst for mixing X and Y. At a similar time by comparing the rate of reactions of both the reaction it can also find out whether A is a catalyst or not.  

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link: