A radon isotope is radioactive. It undergoes decay by releasing an $\alpha$-particle. What change occurs to the nucleus of a radon atom when the $\alpha$-particle is emitted?
- AIt becomes the nucleus of a different isotope of radon with fewer neutrons.
- BIt becomes the nucleus of a different isotope of radon with more neutrons.
- CIt becomes the nucleus of an element with a higher proton number.
- DIt becomes the nucleus of an element with a lower proton number.