$A(g{)}^{r}2P(g)-.r=0\mathrm{.}1C_A^2,[$gmole $[\frac{\text{:}}{L}*sec\}.0\mathrm{.}5LA0\mathrm{.}01$gmole $.A.$

$\frac{d{n}_A}{dt}=\frac{-0\mathrm{.}1n_A^2}{0\mathrm{.}75-25n_A}$

$t=0n_A=0\mathrm{.}01.13n_A(20).$