Two elements, R and S, have these successive ionization energies (in kJ·mol⁻¹):
R: 577, 1816, 2745, 11 577, 14 829
S: 786, 1577, 3232, 4355, 16 091
Identify which element (R or S) is more likely to belong to Group 13 of the periodic table, and justify your choice in one concise sentence.