The graph illustrates how first ionisation energy changes as proton number increases for several elements. The letters shown are not the true symbols of the elements. Which statement about the elements is correct?
- AP and X are in the same period in the Periodic Table.
- BThe general increase from Q to X is due to increasing atomic radius.
- CThe small decrease from R to S is due to decreased shielding.
- DThe small decrease from U to V is due to repulsion between paired electrons.