Question

________ take place at a very high temperature and hence it is called a thermonuclear reaction.
A) Nuclear fission.
B) Nuclear fusion.
C) Both nuclear fission and fusion.
C) Neither nuclear fission or fusion.

Answer 1

The reactions that take place among nuclei are termed as nuclear reactions. The forces that are present between nuclei can be either of attraction or repulsion and to overcome these forces, high temperature is required so as to carry out the reaction.

Complete step by step answer:
Both nuclear fission and fusion are physical processes that produce a tremendous amount of energy.
i) In nuclear fission, the nucleus of an atom splits into two or more smaller nuclei. A large amount of heat is released during this process and hence is called an exothermic reaction.
These are used in nuclear power reactors (mostly uranium and plutonium). The energy they release turns the water into steam which in turn can rotate the turbines and hence can also help to produce electricity that is carbon free.
Balanced reaction can be given as:

${U_{92}}^{235} + {n_0}^1 \to X{e_{54}}^{137} + S{r_{38}}^{95} + 1{n_0}^1$

Shows the decay of uranium atoms with a release of energy along with other by products (n is neutron and it balances the charge of reaction).
ii) Nuclear fusion is a process where lighter nuclei are combined to form a heavy nucleus.
A force of repulsion between the lighter nuclei which can be overcome by raising the temperature so as to combine them together.
e.g atoms of hydrogen fuse to produce helium. These reactions cannot be sustained for long due to their high energy requirements.
Balanced reaction can be given as:

${H_1}^2 + {H_1}^3 \to H{e_2}^4 + {n_0}^1$

Tritium $\left( {{H_1}^3} \right)$ and deuterium $\left( {{H_1}^2} \right)$ fuse to form helium $\left( {H{e_2}^4} \right)$
(n is neutron and it balances the charge of reaction)
As we can see high temperature is required during the process of ‘Nuclear Fusion’ to break the old bonds and form the new ones. Therefore, it can be called a thermonuclear reaction.

Thus the correct option is option B).

Note: Fusion generally takes place in lighter nuclei.
Thermo refers to heat and hence indicates a high temperature.
Remember: The reactions in which heat is released are called exothermic whereas in which heat is absorbed are called endothermic reactions.
Therefore, the process of nuclear fusion takes place at high temperatures.