\(R \rightarrow P\)
\(-x x=\frac{2}{3} a \)
\(a-\frac{2}{3} a\)
According to the half-life of a first order reaction,
\(t=\frac{2.303}{k} \log \frac{ a }{ a - x }\)
\(=\frac{2.303}{4.3 \times 10^{-4}} \log \frac{ a }{ a / 3}\)
\(=\frac{2.303}{4.3 \times 10^{-4}} \log 3\)
\(=2.5 \times 10^{3} \,sec\)
(આપેલું છે$: \ln 10=2.3, R =8.3 \,J\, K ^{-1} \,mol ^{-1}, \log 2=0.30$ )