A radioactive decay occurs in the unstable nucleus of an element. Its proton number does not change. Which statement correctly describes this radioactive decay event?
- AThe nucleus emits an $\alpha$-particle.
- BThe nucleus emits a $\beta$-particle.
- CThe nucleus emits $\gamma$-radiation.
- DThe nucleus emits an $\alpha$-particle, a $\beta$-particle and $\gamma$-radiation together.