The equation shows an isotope of radium Ra decaying into an isotope of radon Rn, together with the emission of particle X. $^ {226}_{88}\text{Ra} \rightarrow ^ {222}_{86}\text{Rn} + X$. What is particle $X$?
- A$^0_{-1}e$
- B$^1_1\text{H}$
- C$^4_2\text{He}$
- D$^1_0\text{n}$