Which laboratory activities involve chemical changes? check all that apply.

leaving a copper penny in vinegar until it turns green
boiling saltwater for several minutes until only solid salt remains
extracting iron filings from a sand mixture using a magnet
crushing a rock with a hammer to extract mineral deposits
putting an iron nail outside for a month and observing changes

The green that grows on the copper penny, and the rust that forms
on the iron nail, are chemical changes.

Boiling salt water away, extracting iron filings from a sand mixture with
a magnet, and crushing a rock with a hammer, are physical changes.

Extracting iron filings from a sand mixture with a magnet isn't a change
at all.  That's just separating things that started out mixed.

Wind or electric energy force force of friction