Answer:
Sulfur
Step-by-step explanation:
A non-metal in the third period that should have chemical properties similar to oxygen is sulfur.
This is because elements in the same group/family have similar chemical properties.
- Chemical properties is predicated on the number of valence electrons within an atom.
- The number of valence electrons is the number of outermost shell electrons within an atom.
- Elements combines with one another using these valence shell electrons.
- Since sulfur is in the third period and the same vertical group as oxygen, they have similar chemical properties.