Argon is very unreactive as it is a noble gas. Its common oxidation number is zero.
It shows some oxidation numbers. Generally it shows +4 oxidation numbers.
0 in the elemental form, +2 and +4 in its compounds
It is a gas. Generally it shows -2 oxidation number.
Argon doesn't form compounds and so its oxidation number is zero
-1 in bromide (most common). It can exhibit oxidation numbers from -1 to +7 (in HBrO4)
-1 is most common in chlorides. However chlorine can exhibit oxidation numbers up to +7 in its compounds.
The most common oxidation numbers of fermium, Fm, are +2 and +3, though there are no stable isotopes (half-life times shorter than 100 days)
Bromine has an oxidation number of negative one, except when with oxygen or flourine.
Formulas for compounds
It depends on the compound. Lead can have an oxidation state of either 2+ or 4+
-1 is most common, but Cl can exhibit oxidation numbers from -1 to +7 in its compounds.
Ar 40 is the most common isotope, accounting for 99.6% of the total (by weight).