(i) The change in the concentration (R) vs. time (t) figure illustrated here shows a zero order reaction, for which the reaction's rate is proportional to the reactant concentration's zero power. (ii) The rate constant for a reaction with zero orders is given as, $[R]=[R]^0 - k t$ Therefore, the slope of the curve representing the fluctuation in the concentration (R) vs. time ( $t$ ) plot is opposite the reaction's rate constant.