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

${\mathrm{SO}}_2$​ and ${\mathrm{CO}}_2$​ both turn lime water (A) 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 (C) turning it black. These gases are to be detected in order by using these reagents. The order is (B),(A),(C). (B) will absorb ${\mathrm{SO}}_2$ first. Thus, it will be removed from the mixture. Then (A) will absorb ${\mathrm{CO}}_2$​. Thus, it will also be removed from the mixture. Now (C) will absorb oxygen.

Sequence is: $$\begin{gathered} {\mathrm{SO}}_2> { \mathrm{CO}}_2> {\mathrm{O}}_2 \\ \text{ (More acidic) , (Less acidic) (Neutral) } \end{gathered}$$