Question

question #2 which set of observations is evidence that a chemical reaction took place in a mixture? a color b density c reactivity d volume

Explanation:

Chemical properties are characteristics that describe how a substance changes in a chemical reaction. Reactivity indicates how a substance will react with other substances, which is a chemical property. Volume, density, and color are physical properties. For evidence of a chemical reaction in a mixture, reactivity - such as a new substance being formed due to a reaction - is an indicator.

Answer:

Question #1: C. reactivity
Question #2: C. reactivity