Which equation shows the second ionisation energy of an element X?
- A$\text{X(g)} \rightarrow \text{X}^{2+}\text{(g)} + 2\text{e}^-$
- B$\text{X}^+\text{(g)} \rightarrow \text{X}^{2+}\text{(g)} + \text{e}^-$
- C$\text{X(g)} + 2\text{e}^- \rightarrow \text{X}^{2-}\text{(g)}$
- D$\text{X}^-\text{(g)} + \text{e}^- \rightarrow \text{X}^{2-}\text{(g)}$