Step-by-step explanation:
If we change the concentration of Potassium since we take KI solution, concentration of I- changes, then the rate changes accordingly
Rate = k[H2O2 ]^a[I-]^b [H+]^c
The concentrations of I- and H+ are held constant in the procedure
thus to study the rate of the reaction, concentration of KI solution has to be constant only the peroxide solution varies.