The half-life of a first-order reaction is $2000$ years. If the concentration after $8000$ years is $0.02 \, M$,then the initial concentration was $........... \, M$.

For a first-order reaction $A \rightarrow B$,if the rate constant is $k$ and the initial concentration of reactant $A$ is $0.5 \ M$,what is its half-life period?

If the rate constant for a first order reaction is $k$,then find the time required for completion of $80 \%$ of the reaction.

How much time is required for a first-order reaction to be $3/4$ complete?

The time taken for $10 \%$ completion of a first order reaction is $20 \ min$. Then, for $19 \%$ completion, the reaction will take (in $min$)

The half-life period of a first-order chemical reaction is $6.93 \, \text{min}$. The time required for the completion of $99 \%$ of the chemical reaction will be ........ $\text{min}$. $(\log 2 = 0.301)$