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.