salt and pepper water and sugar iron nails and pennies baking soda and vinegar
I gave my students this multiple choice question: Materials combine chemically or physically. Which materials form a new substance when chemically combined?

Only one answer is correct among these 4 choices:
- salt and pepper
- water and sugar
- iron nails and pennies
- baking soda and vinegar

Could you tell me which one is correct?

baking soda and vinegar