Question

The phenomenon of radioactivity is associated with:
A: Decay of nucleus
B: Fusion of nucleus
C: Emission of electrons or protons
D: Rearrangement in the extranuclear electron

Answer 1

Hint: Radioactive substances are the substances which decay naturally. When they decay they release alpha particles, beta particles, and gamma radiations. Some examples of radioactive substances are cesium, uranium, plutonium, etc.

Complete step by step answer:
We know radioactive substances are the substances which decay naturally. Radioactive elements have unstable nuclei due to which they decay naturally and the phenomenon is called radioactivity. When they decay some substances are emitted. In this process, the unstable nucleus loses its energy by emitting radiation. Most common types of decays are $\alpha - $decay, $\beta - $ decay and $\gamma - $ decay. In all these decays one or more particles are emitted. According to theories, it is impossible to predict when an atom will decay. It is a random process. The decaying nucleus is called the parent nucleus and the nucleus which is emitted is called the daughter nucleus. $\alpha - $Decay occurs when there is emission of $\alpha - $particle. Helium nucleus is $\alpha - $ particle. $\beta - $Decay occurs in two ways beta-minus decay and beta-plus decay. In beta-minus decay, the nucleus emits an electron and an antineutrino (in this process the neutron changes to the proton). In beta-plus decay, the nucleus emits a proton and a neutrino. In $\gamma - $ decay nucleus first decays by $\alpha - $decay or $\beta - $decay then daughter nuclei (which is present in excited state) emits gamma-ray photons to become stable. In all these processes there is a decay of the nucleus; this means the process of radioactivity is associated with the decay of the nucleus.

So, the correct answer is option A that is Decay of the nucleus.


Note:
There is a process called electron capture. In this process, the nucleus captures an orbiting electron which causes a proton to convert into a neutron. A neutron and gamma-ray is also emitted in this process.