(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, $\left[\mathit{R}\right]={\left[\mathit{R}\right]}^0-\mathit{k}\mathit{t}$
Therefore, the slope of the curve representing the fluctuation in the concentration (R) vs. time ( $\mathit{t}$ ) plot is opposite the reaction's rate constant.