Question

How can uranium $ - 238 $ decay to plutonium $ - 239 $ but its mass still increases?
A $ ^{238}U $ undergoes fission, then beta decay.
B $ ^{238}U $ exhibits alpha emission.
C $ ^{238}U $ undergoes neutron capture, then beta decay.
D $ ^{238}U $ undergoes fusion.

Answer 1

Hint :Uranium is a chemical element which occurs in nature, it is extracted from minerals such as uraninite. It has an atomic number $ 92 $ . Plutonium has atomic number $ 94 $ , plutonium occurs naturally but at very low concentration hence it is created in reactors from uranium.

Complete Step By Step Answer:
Let's start with the things we know, so we have mentioned atomic number of uranium is $ 92 $ , uranium $ - 238 $ isotope has total number of neutrons $ = 238 - 92 = 146 $
Similarly, plutonium has atomic number $ 94 $ and has isotope plutonium $ - 239 $
So let's find of number of neutrons in plutonium, number of neutrons $ = 239 - 94 = 145 $
So basically uranium $ - 238 $ undergoes neutron capture contrary at this point, but the main reason is beta decay because of which beta decay occurs, to be more clear two beta decay takes place.
When uranium $ - 238 $ capture neutron it becomes uranium $ - 239 $
 $ {}_{92}^{238}U + {}_0^1n \to {}_{92}^{239}U $
When the nuclide decays with beta decay, a neutron located inside the nucleus gets converted to a proton and an electron and antineutrino are emitted.
This changes atomic number but will leave its mass number as it is, that means the number of neutrons and protons inside the nucleus remains unchanged.
The first beta decay reaction will takes place
 $ {}_{92}^{239}U \to {}_{93}^{239}U + {}_{ - 1}^0e + \overline {{v_e}} $
Now, uranium $ - 239 $ will get decay into neptunium $ - 239 $ with beta decay. So the second beta decay will takes place
 $ {}_{93}^{239}Np \to {}_{94}^{239}Pu + {}_{ - 1}^0e + \overline {{v_e}} $
Option C is correct.

Note :
Uranium is a heavy metal, uranium and plutonium were used to make bombs. After doing research on them they now play a very significant role for making electricity and radioisotopes. Both of these are hazardous when inhaled.