Question

Which of the following is a nuclear reaction?
A. Two hydrogen atoms combine to form hydrogen molecule
B. Sodium atom gives up an electron to become sodium ion
C. Water splits up into hydrogen and oxygen by electrolysis
D. Isotopes of hydrogen nuclei combine to form helium nuclei

Answer 1

A nuclear reaction is that reaction which involves the change in the nucleus of the atom. A chemical reaction is that reaction which is not concerned with the nucleus but only with the orbital electrons surrounding the nucleus.

Complete step by step answer:
Let us define a chemical reaction and a nuclear reaction to understand the differences between them.
An atom consists of a nucleus containing neutrons and protons with electrons which revolve around the nucleus in fixed circular orbits.
A chemical reaction is the reaction which involves only the orbital electrons of an atom. Two or more atoms interchange electrons between them which lead to formation of new bonds between atoms changing the physical properties of the material.
A nuclear reaction involves the nucleons: protons and neutrons. These nucleons may undergo disintegration or may combine with each other creating new particles. This leads to an increase or decrease in the number of nucleons which may convert a nuclei into its isotope, isobar, etc.
Out of the given options, only option D represents a nuclear reaction as it is an example of fusion of nuclei creating a new nucleus.

Note:
1. There is no change in the identity of an atom when a chemical reaction takes place but in case of nuclear reactions, the identity of the atom itself changes.
2. All other options are examples of chemical reaction as there is change only in the electrons around the nucleus. When two atoms combine with each other, there is bond formation between the electrons of the atoms but when two nuclei combine, there is change in the number of nucleons of the nucleus of atom.