What is the time required for completion of $90 \%$ of a first order reaction?

The time taken for $10 \%$ completion of a first order reaction is $20$ minutes. The time required for the completion of $19 \%$ of the same reaction in minutes is

The reaction $A_{(g)} \to 2B_{(g)} + C_{(g)}$ obeys the rate law,$r = K[A]$ where $K = 0.023 \ s^{-1}$. If $2.5 \ moles$ of $A$ were taken in a $5 \ L$ flask,how many moles of $A$ would remain left after $50 \ seconds$?

The reaction $2H_2O_2 \to 2H_2O + O_2$ is a

For two first-order reactions:
$A \rightarrow \text{Products}$
$B \rightarrow \text{Products}$
If at the same time,$50\% \, B$ has reacted and $94\% \, A$ has reacted,calculate the ratio $K_1/K_2$.

For a first-order reaction involving gaseous reactants and gaseous products,what will be the unit of its rate constant?