For a reversible chemical reaction where the forward process is exothermic, which of the following statements is correct?

An endothermic reaction $A \to B$ has an activation energy of $15 \ kcal/mol$ and an enthalpy change of reaction of $5 \ kcal/mol$. The activation energy of the reverse reaction $B \to A$ is ......... $kcal/mol$.

$A$ given sample of milk turns sour at room temperature $(27^{\circ} C)$ in $5 \ h$. In a refrigerator at $-3^{\circ} C$,it can be stored $10$ times longer. The energy of activation for the souring of milk is

Select the correct statement.

Consider the following transformation involving first order elementary reactions in each step at constant temperature as shown below.
$A + B \underset{\text{Step } 3}{\overset{\text{Step } 1}{\rightleftharpoons}} C \xrightarrow{\text{Step } 2} P$
Some details of the above reaction are listed below.

Step	Rate constant $(s^{-1})$	Activation energy $(kJ \ mol^{-1})$
$1$	$k_1$	$300$
$2$	$k_2$	$200$
$3$	$k_3$	$Ea_3$

If the overall rate constant of the above transformation $(k)$ is given as $k = \frac{k_1 k_2}{k_3}$ and the overall activation energy $(E_a)$ is $400 \ kJ \ mol^{-1}$,then the value of $Ea_3$ is $\qquad$ $kJ \ mol^{-1}$ (nearest integer).

The rate constant of a reaction at $500 \ K$ and $700 \ K$ are $0.02 \ s^{-1}$ and $0.2 \ s^{-1}$ respectively. The activation energy of the reaction (in $kJ \ mol^{-1}$) is $(R=8.3 \ J \ K^{-1} \ mol^{-1})$