An element A decays into element C by a two-step process:

$$\begin{gathered} \mathrm{A}\to \mathrm{B}+{}_2\mathrm{He}^4 \\ \mathrm{B}\to \mathrm{C}+2{\mathrm{e}}^{-} \end{gathered}$$

Then

• A

  A and C are isotopes

• B

  A and C are isobars

• C

  A and B are isotopes

• D

  A and B are isobars