In a first order reaction,the concentration of the reactant decreased from $0.4 \, M$ to $0.1 \, M$ in $20 \, \min$. The rate constant of the reaction will be:

Consider the first-order gas-phase decomposition reaction given below:
$A_{(g)} \longrightarrow B_{(g)} + C_{(g)}$
The initial pressure of the system before the decomposition of $A$ was $P_i$. After time $t$,the total pressure of the system increased by $x \ units$ and became $P_t$. The rate constant $k$ for the reaction is given as:

Time required for $90 \%$ completion of a first order reaction is '$x$' minute. Calculate the time required to complete $99.9 \%$ of the reaction at the same temperature.

The half-life period of a first order reaction is $100 \, \text{sec}$. The rate constant of the reaction is

The decomposition of substance $A$ in a solution follows first-order kinetics. Vessel-$I$ contains $1 \ L$ of $1 \ M$ solution of $A$. Vessel-$II$ contains $100 \ mL$ of $0.6 \ M$ solution of $A$. If the concentration of $A$ in Vessel-$I$ becomes $0.25 \ M$ in $8 \ hr$,then the time required for the concentration of $A$ in Vessel-$II$ to become $0.3 \ M$ is ......... $hr$.

$N_2O_5 \rightarrow 2NO_{2(g)} + \frac{1}{2}O_{2(g)}$ is a first order reaction. $k = 5 \times 10^{-4} \ s^{-1}$. The initial concentration of $N_2O_5 = 0.2 \ mol \ L^{-1}$. After how much time will its concentration be $25 \%$ of the initial concentration (in $s$)?