A substance contains a radioactive isotope that decays only through the emission of $\alpha$-particles at a rate of $100\,\text{s}^{-1}$. Which statement about this substance is true?
- AThe number of atoms in the material diminishes at a rate of $100\,\text{s}^{-1}$.
- BThe number of neutrons in the material diminishes at a rate of $100\,\text{s}^{-1}$.
- CThe number of nucleons in the material diminishes at a rate of $400\,\text{s}^{-1}$.
- DThe number of protons in the material diminishes at a rate of $100\,\text{s}^{-1}$.