${\mathrm{SO}}_2$ and ${\mathrm{CO}}_2$ both turn lime water $\left(\mathrm{A}\right)$ milky, ${\mathrm{SO}}_2$ also turns ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7/{\mathrm{H}}^{+}$ $\left(\mathrm{B}\right)$ green while ${\mathrm{O}}_2$ is soluble in pyrogallol $\left(\mathrm{C}\right)$ turning it black. These gases are to detected in order by using these reagents. The order is