Question

which laboratory activity involves a chemical change?
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

Explanation:

A chemical change involves a transformation that results in the formation of new substances. Leaving a copper penny in vinegar until it turns green is a chemical change because a new substance (a copper - vinegar reaction product) is formed. Crushing a rock is a physical change (changes form but not substance). Extracting iron filings with a magnet is a physical separation (no new substance). Boiling saltwater is a physical change (evaporation of water, leaving salt).

Answer:

leaving a copper penny in vinegar until it turns green