104 ml of ethene, C2H4 is burned in 408 ml of oxygen, producing carbon dioxide and some liquid water. Some oxygen remain unreacted. Calculate the volume of carbon dioxide produced and the volume of oxygen remaining

Answer 1

balance the reaction equation.
C2H4+3O2>>>2CO2 + 2H2O

if one assumes temp and pressure remain constant, then the law of volumes indicates one gets two volumes of carbon dioxide for each volume of ethene.
So ...208ml

volume of O2 remaining, you used 3*104ml, so subtract that from 408ml.

All this is very wild speculation of constant temp,pressure.