(N/A) $1$. $\alpha-$decay: In this process,an unstable nucleus emits an alpha particle ($^4_2He$ nucleus). The mass number decreases by $4$ and the atomic number decreases by $2$.
General formula: $^{A}_{Z}X \rightarrow ^{A-4}_{Z-2}Y + ^{4}_{2}He + Q$
$2$. $\beta-$decay: In this process,a neutron converts into a proton (or vice versa) emitting an electron/positron and an antineutrino/neutrino. In $\beta^-$ decay,a neutron becomes a proton,emitting an electron $(e^-)$ and an antineutrino $(\bar{\nu})$.
General formula: $^{A}_{Z}X \rightarrow ^{A}_{Z+1}Y + ^{0}_{-1}e + \bar{\nu}$
$3$. $\gamma-$decay: In this process,an excited nucleus releases excess energy in the form of high-energy electromagnetic radiation (photons) without changing its mass number or atomic number.
General formula: $^{A}_{Z}X^* \rightarrow ^{A}_{Z}X + \gamma$