In the series of elements Mg → Si → S → Cl 1) the radii of atoms decrease 2) the number of protons

In the series of elements Mg → Si → S → Cl 1) the radii of atoms decrease 2) the number of protons in the nuclei of atoms decreases 3) the number of electronic layers in atoms increases 4) the highest oxidation state of atoms decreases

Elements in this row Mg → Si → S → Cl are located in one period, namely in the third.

The number of protons per revolution increases, so the ordinal number of the elements increases. The number of energy levels or electron layers is unchanged since the elements are in the same period. And the highest oxidation state is equal to the group number, and for magnesium it is +2, for chlorine it is +7. It means it also increases.

Therefore, only option # 1 is suitable. The radius of the atom decreases.