Where are the elements that have the same valence electrons found in the periodic table?

The elements that have the same valence are, mainly, in the same principal groups (principal columns) of the periodic table.

The principal columns are 1, 2, 13, 14, 15, 16, 17 and 18.

For example:

1) the elements with valence 1+ are in the first column:H,  Li, Na, K, Rb, Cs, Fr.

2) The elements with valence 2+ are in the second column: Be, Mg, Ca, Sr, Ba, Ra.

3) The elements with valence 2- are in the column 16: O, S, Se, Te, Pb

But also those elements may have other valences: S, Se and Te, have also valences 2, 4 and 6. And Pb have valences 2 and 4.

4)  The elements with valences 1-, 1, 3, 5 and 7 are in the column 17: Cl, Br, I, At.

F, the first element of group 16, has valence 1- and 1+ 

D.na is the answer hope this

And a) oxygen i believe