If the rate constant of a first-order reaction is $4.606\times10^{-3}\,\mathrm{s^{-1}}$, then the time taken (in seconds) for the concentration of the reactant to decrease from $1.0\,\mathrm{M}$ to $0.1\,\mathrm{M}$ is:}
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For first-order reactions, reducing concentration to one-tenth gives
\[
t=\frac{2.303}{k}.
\]