If each orbital had three electrons instead of two then how many valence electrons would oxygen sulfur and selenium have?

Answer 1

Ultimately, the number of electrons would not change, however, the position of elements of the Periodic Table according to their respective quantizied energy levels would change. For instance, on the periodic table one sharp would have hydrogen helium and lithum, proceeded by two sharp with beryllium, boron and carbon. Two principle would contain nitrogen, oxygen and flouride.

This would merely be an assumption.

Answer 2

Oxygen would have 5 valence electrons, sulfur would have 6 valence electrons, and selenium would have 7 valence electrons. This is because these elements are in Group 16 of the periodic table, which means they normally have 6 valence electrons when orbitals have two electrons each.