\[\_\_\_\_\_\_\_\_\_\_\] is a thermonuclear reaction.
A: Photosynthesis
B: Decay of ${}^{238}U$
C: Nuclear fusion
D: None of these

Answer Verified Verified
Hint: Thermonuclear reactions are related to radioactive elements and their reactions. Such reactions occur at very high temperatures. Temperature is in the order of ${10^{7 \circ }}C$ or higher than this order. These reactions are the main source of production of energy in the sun, nuclear weapons and fusion reactors.

Complete step by step answer:
As the name suggests thermonuclear reactions are reactions related to nuclear reactions which are carried out at high temperature. The temperature order of these reactions are of the order of ${10^{7 \circ }}C$ or even higher. These reactions are actually nuclear fusion reactions. These reactions are the major source of energy in the sun, nuclear weapons and nuclear reactors. This reaction occurs between nucleuses of light elements when they are constituents of gas. As stated earlier these must be at very high temperatures. This reaction occurs most readily between hydrogen isotopes (being the lightest element). In nuclear fusion reactions one or more atomic nuclei or subatomic particles combine to form some other atomic nuclei. By subatomic particles we mean protons or neutrons that are present in the nucleus of an atom. The change in energy in such reactions is calculated from the mass difference of reactants and products formed. Different atomic nuclei have different energies because of different binding energy of atoms. Binding energy is the energy that binds all the subatomic particles together in a nucleus. Now, we know that thermonuclear reactions are actually nuclear fusion reactions.

So, correct answer is option C that is nuclear fusion.

Note: Nuclear fusion is a reaction in which two or more atoms or subatomic particles join to form a new compound and nuclear fission is a type of reaction in which one nucleus decays into two or more daughter nuclei. Sometimes subatomic particles are also released in such fission reactions.