(A) The concentration of the reactant is reduced from $0.6 \text{ mol L}^{-1}$ to $0.2 \text{ mol L}^{-1}$ in $5$ minutes in a first order reaction. Calculate rate constant of the reaction. $(\log 3 = 0.48)$ OR (B) Rate constant $k$ for the first order reaction is $2.54 \times 10^{-3} \text{ s}^{-1}$. Calculate the time required for three-fourth of the reactant to decompose. $(\log 4 = 0.60)$