How does the law of conservation of mass apply to this reaction: c2h4+o2=h2o+co2?

In this case, the total mass of the reactants = total mass of the products. Also, the number of atoms of hydrogen and oxygen in the reactants side and the products side are equal.

that's all I know

because of all the things that happen around the us, many people get into arguments which sadly could get physical, but we should actually make a change for that.

c-14 is carbon-14, or radiocarbon.   it is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.