Respuesta :
Answer: The correct answer is 1.
Explanation: There are various process in which a radioactive nuclei decays:
1) Alpha Decay: In this process, a heavier nuclei decays into lighter nuclei by releasing alpha particle. The mass number is reduced by 4 units.
[tex]_A^Z\textrm{X}\rightarrow _{A-2}^{Z-4}+_2^4\alpha[/tex]
2) Electron capture: In this decay process, a parent nuclei absorbs an electron and gets converted into a neutron. Simply, a proton and an electron combines together to form a neutron. Mass number does not change in this process.
[tex]_A^Z\textrm{X}+_{-1}^0\textrm{e}\rightarrow _{Z-1}^A\textrm{Y}[/tex]
3) Gamma ray emission: It is a decay process in which an unstable nuclei gives excess energy by a spontaneous electromagnetic process. This decay releases [tex]\gamma -radiations[/tex]. This process does not change the mass number.
[tex]_A^Z\textrm{X}^*\rightarrow _A^Z\textrm{X}+_0^0\gamma[/tex]
4) Positron emission: It is a type of decay process, in which a proton gets converted to neutron and an electron neutrino. This is also known as [tex]\beta ^+[/tex]-decay. In this the mass number remains same.
[tex]_A^Z\textrm{X}\rightarrow _{Z-1}^A\textrm{Y}+_{+1}^0e[/tex]
From the above information, we see that only alpha-decay is producing a change in the mass number of the nucleus.
