Consider the following reaction between hydrogen peroxide, hydrogen ions and iodide ions.

$${{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}{\text{(aq)}} + {\text{2}}{{\text{H}}^ + }{\text{(aq)}} + {\text{2}}{{\text{I}}^ - }{\text{(aq)}} \to {{\text{I}}_{\text{2}}}{\text{(aq)}} + {\text{2}}{{\text{H}}_{\text{2}}}{\text{O(l)}}$$

Which changes could be used to investigate the rate of this reaction?

I.     Electrical conductivity

II.     Mass of solution

III.     Colour intensity

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

B