For a first order reaction,
\(t_{1 / 2}=\frac{0.693}{k}\) ( \(k=\) rate constant )
\({\Rightarrow \quad 1} {386=\frac{0.693}{k}}\)
\({\Rightarrow \quad k} {=5 \times 10^{-4} \,\mathrm{s}^{-1}}\)
\({=0.5 \times 10^{-3}\, \mathrm{s}^{-1}}\)
[લો; $R =8.314 \,J\, mol ^{-1}\, K ^{-1}$ In $3.555=1.268$]