Answer: Radioactive elements
Explanation: Radioactivity is the phenomenon in which an unstable nuclei is converted to a stable nuclei by emitting radiations in the form of alpha decay, beta decay and gamma decay.
Alpha decay : When a larger nuclei decays into smaller nuclei by releasing alpha particle. In this process, the mass number and atomic number is reduced by 4 and 2 units respectively.
General representation of alpha decay :
[tex]_Z^A\textrm{X}\rightarrow _{Z-2}^{A-4}Y+_2^4\alpha[/tex]
Beta decay : In this process, a neutron is converted into a proton and an electron. In this decay, the atomic number is increased by 1 unit.
General representation of beta decay :
[tex]_Z^A\textrm{X}\rightarrow _{Z+1}^{A}Y+_{-1}^0e[/tex]
Gamma decay : In this process, the unstable nuclei transformed into stable nuclei by releasing gamma rays. In this process, the mass number remains same.
General representation of gamma decay :
[tex]_Z^A\textrm{X}^*\rightarrow _Z^A\textrm{X}+_0^0\gamma[/tex]
Hence the correct answer is radioactive elements.
