A gaseous mixture containing (X), (Y) and (Z) gases, when passed into acidified K2 Cr2O7 solution, gas (X) was absorbed and the solution was turned green. The remainder gas mixture was then pass through lime water, which turns milky by absorbing gas (Y). The residual gas when passed through alkaline pyrogallol solution, it turned black. Identify gas (X), (Y) and (Z) and explain the reaction involved.
