A nonmetal in the third period that should have chemical properties similar to oxygen.

Sulfur

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.

Aphysical change is one that you can put in and remove like a ham sandwich. the stuff you put in there can be changem its not permanet. a chemical change is on that can't be change thats permanet. like when you make a cake and bake it. you can't get those ingredients back.

Ineed with this also i hope you understand it