Question

what do these two changes have in common?
rust forming on a bicycle frame
salt and vinegar removing tarnish from a penny
select all that apply.
both are changes of state.
both conserve mass.
both are caused by cooling.
both are chemical changes.

Explanation:

1. Analyze "Both are changes of state": Changes of state (like melting, freezing) involve physical state changes (solid/liquid/gas). Rusting and tarnish removal are chemical changes, not state changes. So this is incorrect.
2. Analyze "Both conserve mass": According to the law of conservation of mass, in any chemical or physical change, mass is conserved (mass of reactants = mass of products). Both rusting (chemical reaction: iron + oxygen + water → rust) and tarnish removal (chemical reaction between tarnish and salt/vinegar) are chemical changes, so mass is conserved. This is correct.
3. Analyze "Both are caused by cooling": Rusting is caused by oxidation (reaction with oxygen and water), tarnish removal is a chemical reaction with acid (vinegar) and salt. Cooling is not the cause. So this is incorrect.
4. Analyze "Both are chemical changes": Rusting is the oxidation of iron (new substance, rust, formed). Tarnish removal involves a chemical reaction (tarnish, like copper oxide, reacts with vinegar/salt to form new substances). Both involve new substances, so they are chemical changes. This is correct.

Answer:

B. Both conserve mass
D. Both are chemical changes

(Note: The options are labeled as per typical multiple - choice labeling. If the original problem had different labels, adjust accordingly. The correct options are the ones stating "Both conserve mass" and "Both are chemical changes".)