Which equation represents the $1/4^{th}$ life for a first-order reaction?

For the first-order reaction $N_2O_5 \text{ (in } CCl_4) \rightarrow 2NO_2 + \frac{1}{2}O_{2(g)}$,the rate constant is $6.2 \times 10^{-4} \, s^{-1}$. What will be the rate of reaction when $[N_2O_5] = 1.25 \, mol \, L^{-1}$?

Drug $X$ becomes ineffective after $50 \%$ decomposition. The original concentration of drug in a bottle was $16 \ mg/mL$ which becomes $4 \ mg/mL$ in $12 \ months$. The expiry time of the drug in months is $..........$ Assume that the decomposition of the drug follows first order kinetics.

The half-life period for a first order reaction is $693 \ sec$. The rate constant for this reaction would be: (in $sec^{-1}$)

The reaction $A \to B$ follows first order kinetics. The time taken for $0.8 \ mol$ of $A$ to produce $0.6 \ mol$ of $B$ is $1 \ hr$. What is the time taken for the conversion of $0.9 \ mol$ of $A$ to produce $0.675 \ mol$ of $B$?

$99 \%$ of a first order reaction was completed in $64 \text{ min}$. In how many minutes will $99.9 \%$ of the reaction be complete?