The successive ionization energies in KJ/mol of an element P are 740, 1500, 7000, 10500, 13600, 18000 and 21700. Which ion is the most likely to be formed when P reacts with chloride?

Answer 1

The largest relative increase in IE is in going from 1500 to 7000 kJ/mole. This represents the loss of a third electron, so P is likely to lose only 2 electrons making the ion P²⁺.