The correct sequence of reagents for the preparation of Q and R is :
$$\mathrm{(i)C{r_2}{O_3},770K,20~atm;
(ii)Cr{O_2}C{l_2},{H_3}{O^ + };
(iii)NaOH;(iv){H_3}{O^ + }}$$
$\mathrm{(i)Cr{O_2}C{l_2},{H_3}{O^ + };(ii)C{r_2}{O_3},770K,20~atm;(iii)NaOH;(iv){H_3}{O^ + }}$
$\mathrm{(i)KMn{O_4},O{H^ - };(ii)M{o_2}{O_3},\Delta ;(iii)NaOH;(iv){H_3}{O^ + }}$
$\mathrm{(i)M{o_2}{O_3},\Delta ;(ii)Cr{O_2}C{l_2},{H_3}{O^ + };(iii)NaOH;(iv){H_3}{O^ + }}$
