Because they have one valence electrons, and if they lose this electron they attain an oxidation number of +1
Elements in group 2 have an oxidation number of +2 because they readily lose two electrons to achieve a full outer shell, which is the most stable electron configuration. This results in a +2 oxidation state as they become positively charged cations.
Group 2 or alkaline earth metals
Elements with oxidation numbers of +1 include elements in Group 1 of the periodic table, like hydrogen and sodium. Elements with oxidation numbers of -1 include elements in Group 17, like fluorine and chlorine.
those elements which can donate two electrons will possess plus two oxidation state like calcium , magnesium ,etc...
Beryllium, Magnesium, Calcium, Strontium, Barium, and Radium all have an oxidation state of plus 2.
In KMnO4, Mn has an oxidation number of +7, KNO2 has N with an oxidation number of +3, and H2SO4 has S with an oxidation number of +6. In MnSO4, Mn has an oxidation number of +2, H2O has O with an oxidation number of -2, KNO3 has N with an oxidation number of +5, and K2SO4 has S with an oxidation number of +6.
It would have been plus seven if possible, however the maximum is the number of valence electron of sulfur to be donated, so that is clearly +6 (six!).In H2S2O7 the oxidation number is +6
Mn increase in oxidation number from +4 to +7.
In the compound H2S, hydrogen has an oxidation number of +1, and sulfur has an oxidation number of -2.
Potassium's minimum oxidation number is zero.Its maximum is plus one.
An element with an oxidation number of +1 is typically found in group 1 of the periodic table, such as sodium (Na) or potassium (K). An element with an oxidation number of -1 is typically found in group 17 of the periodic table, such as chlorine (Cl) or fluorine (F).
-2