d
\({{K}_{2}}=\frac{1}{t}\frac{x}{a(a-x)}\)

Let  \(a=1\),

\({{K}_{2}}=\frac{1}{t}\frac{x}{(1-x)}\)

\(=\frac{1}{3000}\left( \frac{0.6}{1-0.6} \right)\)

\(=\frac{1}{3000}\times \frac{0.6}{0.4}=\frac{1}{2000}\)

\(20\%\) પૂરી થવા માટે 

\(\therefore \,\text{t}=\frac{\text{1}}{{{\text{k}}_{\text{2}}}}\frac{x}{a(a-x)}\)

\(=2000\times \frac{0.20}{0.80}\)

\(=500\,\sec\)