Half-life of a first order reaction is 20 seconds and initial concentration of reactant is 0.2 M . The concentration of reactant left after 80 seconds is

$$ \text { In the given graph, } \mathrm{E}_{\mathrm{a}} \text { for the reverse reaction will be } $$

For the reaction $2 \mathrm{~N}_2 \mathrm{O}_{5(\mathrm{~g})} \rightarrow 4 \mathrm{NO}_{2(\mathrm{~g})}+\mathrm{O}_{2(\mathrm{~g})}$ initial concentration of $\mathrm{N}_2 \mathrm{O}_5$ is $2.0 \mathrm{molL}^{-1}$ and after 300 min , it is reduced to $1.4 \mathrm{molL}^{-1}$. The rate of production of $\mathrm{NO}_2\left(\mathrm{in} \mathrm{molL}^{-1} \mathrm{~min}^{-1}\right)$ is

For the reaction, $A \rightleftharpoons B, E_a=50 \mathrm{~kJ} \mathrm{~mol}^{-1}$ and $\Delta H=-20 \mathrm{~kJ} \mathrm{~mol}^{-1}$. When a catalyst is added $E_a$ decreases by $10 \mathrm{~kJ} \mathrm{~mol}^{-1}$. What is the $E_a$ for the backward reaction in the presence of catalyst?