Answer
C. It becomes plutonium-239
Explanation
Absorption of a neutron in the uranium-238 nucleus yields uranium-239, which decays after 23.47 minutes through electron emission into neptunium-239 and ultimately, after 2.356 days, into plutonium-239.
Note that all of the compounds in the chemical reaction are gases. Through avogadro's law, we know that each of these gases take up a proportional amount of space. Therefore, since the molar ratio of ethene and oxygen is 1:3, than 810 Liters of Oxygen gas must react with 270 liters of C2H4(ethene).