Which statement describes a chemical change? 1. alcohol evaporates. 2. water vapor forms snowflakes. 3. table salt (nacl) is crushed into powder. 4. glucose (c6h12o6) and oxygen produce co2 and h2o.

4. Glucose (C6H12O6) and oxygen produce CO2 and H20. All other options are physical changes.

Chemical changes are changes that produce new substances and are not easily reversed(return to its actual or previous form).
Physical changes on the other hand are changes that form no new products but can easily be reversed( return to its actual or previous form).

Choice 1,2, and 3 all are physical as there are no new products formed but only change from one state to another.
Choice 4 is chemical as new products are formed.