(i) Represent the change in the nucleus of a radioactive element when a β particle is emitted.

(i) If a radioactive nucleus P with mass number A and atomic number Z emits a β particle to form a daughter nucleus Q with mass number A and atomic number Z + 1, the change can be represented as follows:

$$\begin{matrix} _{Z}^{A}\text{P} & \longrightarrow & _{Z+1}^{\space \space \space \space \space A}\text{Q} & + & \space _{-1}^{\space \space \space 0}\text{e} \\ \footnotesize{\text{Parent}} & & \footnotesize{\text{Daughter}} & & \footnotesize{\text{Beta}} \\ \footnotesize{\text{nucleus}} & & \footnotesize{\text{nucleus}} & & \footnotesize{\text{particle}} \end{matrix}$$

ii) Elements with same mass number A, but different atomic number Z are called isobars.

iii) The nucleus of an atom tend to be radioactive when the number of neutrons is more than the number of protons. The nucleus thus becomes unstable and in order to gain stability it tends to emit α, β, γ radiations.