Which process is a chemical change​

Silver tarnishes as silver metal reacts with hydrogen sulfide, h2s, in the air. in this reaction, dark silver sulfide, au2s, covers the surface of silver. when silver is polished, this coating of silver sulfide can be removed from the surface. this makes the silver shiny again. enter the coefficients that balance the tarnishing reaction equation. (type 1 for no coefficient.)

Find the number of grams of hcl needed to react completely with .50 moles of magnesium.

Which of the following is not an assumption that scientists must make about the natural world? a. regularity b. causality c. predictability d. plausibility