JEE Advanced 2025 · Paper 2, Chemistry question 12

Consider a reaction $A + R \longrightarrow \textit{Product}$. The rate of this reaction is measured to be $k[A][R]$. At the start of the reaction, the concentration of $R$, $[R]_0$, is 10-times the concentration of $A$, $[A]_0$. The reaction can be considered to be a pseudo first order reaction with assumption that $k[R] = k'$ is constant. Due to this assumption, the relative error (in %) in the rate when this reaction is 40 % complete, is _____.

[$k$ and $k'$ represent corresponding rate constants]