12mll OF A GASEOUS HYDROCARBON WAS EXPLODED WITH 50ml OF OXYGEN .THE VOLUME AFTER EXPLOSION WAS 32 ml. ON TREATMENT WITH KOH THE VOLUME REDUCED TO 8ml. THEN FORMULA OF HYDROCARBON IS

1. C_​2H₂
2. C₂H₆
3. C₃H₈

C_xH_y + O₂ $\to$CO₂ + H₂O
​Volume of (CO₂ + unreacted O₂) = 32 ml.
As CO₂  can be absorbed by KOH .  When this 32 ml. mixture is treated with KOH, it is reduced to 8 ml.
Therefore amount of CO₂ formed = 32 ml. - 8ml.= 24 ml.
Amount of unreacted O₂ = 8 ml.
Volume of O₂ reacted = 50 ml - 8 ml = 42 ml.
Volume of hydrocarbon = 12 ml.
Apply Principle of Atom Conservation (POAC) on C we get:
X moles of C_x H_y = 1 no. of moles of CO₂ 
X $\times$12 ml = 1 x 24 ml
X = 24/12 = 2