50 ml of gaseous hydrocarbon were mixed with 200 ml of oxygen and set on fire. The volume of the resulting gas mixture

50 ml of gaseous hydrocarbon were mixed with 200 ml of oxygen and set on fire. The volume of the resulting gas mixture was left 125 ml, and after passing it through an alkali solution, it decreased to 25 ml. Determine the formula of the initial gaseous substance.

4CxHy + (4x + y) O2 = 4xCO2 + 2yH2O
V (CO2) = 100ml; If we take into account that water is condensing (this should have been indicated in the condition), then the volume of reacted О2 was: 200-25 = 175 ml;
let’s make a proportion:
(4x + y): 175 = 4x: 100
y = 3x;
If X = 1, then y = 3, and then the formula is -CH3 (but there is no such hydrocarbon!), Therefore we multiply everything by half
if X = 2, then y = 6, hence the formula is C2H6 (ethane).