\( - \frac{1}{2}\frac{{dS{O_2}}}{{dt}}\, - \,\frac{{d{O_2}}}{{dt}} - \frac{1}{2}\frac{{dS{O_3}}}{{dt}}\)
\(\therefore \,\,\frac{{dS{O_2}}}{{dt}}\, = -\,2 \times \frac{{d{O_2}}}{{dt}}\)
\(=\,-\,2\times 2.5\times 10^{-4}\)
\(=\,-\,5\times 10^{-4}\,mol\,L^{-1}\,s^{-1}\)