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 ....... $s$.

$A$ first order reaction has a rate constant $1.1 \times 10^{-3} \ s^{-1}$. How long will $6 \ g$ of this reactant take to reduce to $3 \ g$ (in $s$)?

Time required for completion of $99.9 \%$ of a First order reaction is . . . . . . times of half life $(t_{1/2})$ of the reaction.

Calculate the amount of reactant in percent that remains after $60 \ min$ in a first-order reaction. $(k = 0.02303 \ min^{-1})$ (in $\%$)

An organic compound undergoes first order decomposition. The time taken for its decomposition to $\frac{1}{8}$ and $\frac{1}{10}$ of its initial concentration are $t_{1/8}$ and $t_{1/10}$ respectively. What is the value of $\frac{t_{1/8}}{t_{1/10}}$? $[\log 2 = 0.30]$

Hydrolysis of $DDT$ is a first order reaction,its half-life is $10 \ years$. Time required to hydrolyse $10 \ g$ of $DDT$ to half is ......... $years$.