iodine, iron, nickel helium, carbon, gold sodium, chromium, copper phosphorus, nitrogen, oxygen
I gave my students this multiple choice question: Which set of elements contains only metals?

Only one answer is correct among these 4 choices:
- iodine, iron, nickel
- helium, carbon, gold
- sodium, chromium, copper
- phosphorus, nitrogen, oxygen

Could you tell me which one is correct?

sodium, chromium, copper