In which equations of the series H2S, N2, HI, H2, NaF, Cl2, CaF the oxidation state is zero?

These substances can be divided into 3 groups:

the first group – substances with an ionic bond -NaF, CaF2, this bond is very polar, metals always have a “+” charge, non-metals always have “-“;

the second group – substances with a covalently polar bond – H2S, HI, is also always polar, the more electronegative element has a charge “-” in these examples it is S with charge “-2” and I with charge “-1”, and the other element of the molecule has a “+” charge;

the third group of substances: Cl2, H2, N2. These molecules are composed of two elements of the same electronegativity. These substances are called simple and their oxidation state is zero.