6. iron and sulfur are heated and form a non-magnetic shiny grey substance. physical or chemical change

When iron and sulfur are heated, and then it forms a non-magnetic shiny grey substance, then it is a Chemical Change because a new SUBSTANCE called Iron Sulfide was formed.

To add, chemical change is usually an irreversible chemical reaction involving the rearrangement of the atoms of one or more substances and a change in their chemical properties or composition, resulting in the formation of at least one new substance.