Question

The phenomenon of radioactivity
A. is an exothermic change which increase or decrease with temperature
B. increase on applied pressure
C. is a nuclear process does not depend upon temperature
D. none of these

Answer 1

Radioactivity is a process of spontaneous disintegration or breaking of unstable atomic nucleus by the emission of radiation like $\alpha -\text{ray}$ or $\beta -\text{ray}$or $\lambda -\text{ray}$. The radioactive process is spontaneous that means it occurs by itself. It cannot be initiated, stopped, accelerated or decelerated by external factors like by changing chemical conditions or by changing physical conditions like temperature or pressure.

Complete step by step answer:
Naturally occurring heavy nuclei are unstable so it breaks up to stable light nuclei. It spontaneously emits particles without the help of any outside agency like temperature and pressure. So radioactivity is a nuclear process and it does not depend upon temperature.

So the correct option is C. is a nuclear process and does not depend upon temperature.

Additional Information: Stability of nuclei is determined by $\dfrac{N}{Z}$ value. Where $N=\text{ Number of neutrons in a nucleus}$ and $Z=\text{ Number of protons in a nucleus}$. For light nuclei $N=Z$so $\dfrac{N}{Z}=1$. As the proton number increases the interatomic repulsion between the protons increases so more neutrons are required to make the nucleus. So $\dfrac{N}{Z}$ increases for heavier nuclei and becomes $1.6$ for heaviest stable nucleus ${}_{83}^{209}Bi$. After $Z>83$ there is no stable nucleus and they all decay to form stable nuclei or stable isotopes. The nuclides which undergo radioactive disintegration are called radioactive nuclides.

Note: Note that radioactivity is independent upon any physical condition but it depends upon nuclear bombardment. Also heavy nuclei achieve stability by increasing neutron number so that more neutrons are available for pairing with protons to make it stable. But a nucleus with too many neutrons is unstable because not enough neutrons are paired with protons so it disintegrates to become stable, or to become heavy nuclei.
An atom is represented by ${}_{Z}^{A}X$ where $A=\text{ Mass number}$, $Z=\text{ Atomic number or number of protons}$, then number of neutrons is given by $N=A-Z$.