Half-life of a first order reaction is $20 \ s$ and initial concentration of reactant is $0.2 \ M$. The concentration of reactant left after $80 \ s$ is (in $M$)

Which of the following expressions is correct for a first-order reaction? $(CO)$ refers to the initial concentration of the reactant.

For a first order reaction,the concentration of reactant decreases from $0.2 \ M$ to $0.1 \ M$ in $100 \ minutes$. What is the rate constant of the reaction?

The half-life of a substance in a certain enzyme-catalysed reaction is $138 \; s$. The time required for the concentration of the substance to fall from $1.28 \; mg \; L^{-1}$ to $0.04 \; mg \; L^{-1}$ is ....... $s$.

For a first order reaction, the half-life is $5 \text{ hour}$. What time is required to reduce $10 \text{ g}$ of reactant to $2.5 \text{ g}$ (in $\text{ hour}$)?

In a first-order reaction of the type: $A_{(g)} \to 2B_{(g)}$,the initial pressure is $P_i$ and the total pressure at time $t$ is $P_t$. The rate constant $k$ can be expressed as: