This work discusses the effect of gas mixing ratio on the HBr/X (X=Ar, He, or N-2) plasma parameters, steady-state densities, and fluxes of active species in the planar inductively coupled plasma reactor. The investigation combined plasma diagnostics by Langmuir probes and a global (zero-dimensional) plasma model with Maxwellian approximation for the electron energy distribution function. The dilution of HBr by Ar results in a maximum effect on the HBr electron impact dissociation kinetics and provides a favorable condition for an ion-assisted chemical reaction.