If the half-life $(t_{1/2})$ of a first-order reaction is $20 \ minutes$,what fraction of the reactant remains after $40 \ minutes$?

The half-life of a first-order reaction is

In a first order reaction,the concentration of the reactant decreases from $0.8 \ M$ to $0.4 \ M$ in $15 \ min$. The time taken for the concentration to change from $0.1 \ M$ to $0.025 \ M$ is .......... $min$.

The plot of $t_{1/2}$ versus $[R]_0$ for a reaction is a straight line parallel to the $x$-axis. The unit for the rate constant of this reaction is:

Calculate the rate constant of a first-order reaction having a half-life of $1 \text{ minute } 40 \text{ seconds}$.

The value of the velocity constant for a first-order reaction is $3.46 \times 10^{-3} \ min^{-1}$. The time for half-change is ........ $min$.