The third-period elements have the following atomic radii (values in pm):
Na 186 Mg 160 Al 143 Si 118 P 111 S 103 Cl 99 Ar 71
An unknown element X in this period has an atomic radius of 103 pm and a first ionization energy of approximately 1 000 kJ·mol⁻¹. Which element is X most likely to be?
a) Cl
b) P
c) S
d) Ar