The activation energy for the reaction $X \rightarrow Y$ is $150\text{ kJ mol}^{-1}$. The change in enthalpy for the above reaction is $-135\text{ kJ mol}^{-1}$. Then the activation energy for $Y \rightarrow X$ is

For a 1st order change $R \rightarrow P$, the concentration of Reactant R changes from $0.1$ M to $0.025$ M in $40$ minutes. The rate of reaction when the concentration of R is $0.01$ M is ____

For a reaction having three steps, the overall rate constant is $k = \dfrac{k_1 k_2}{k_3}$. The values of $E_{a_1}, E_{a_2}$ and $E_{a_3}$ (activation energies stepwise) are $40$, $50$ and $60$ kJ mol$^{-1}$ respectively. Then the overall $E_a$ (activation energy) of the reaction is ____

Which one of the following graph is not applicable for a 1st order reaction ($R \rightarrow P$)?