Question

which most likely has occurred when two or more liquid substances that have been combined produce a gas?
a. a change in size or shape of the substances
b. at least one substance that dissolves in another
c. a change in color of the substances observed
d. production of a new substance with new properties

Explanation:

When two or more liquid substances are combined and produce a gas, a chemical reaction has likely occurred. A chemical reaction results in the production of a new substance with new properties. A change in size or shape (A) is a physical change. One substance dissolving in another (B) is a physical change (formation of a solution). A change in color (C) can sometimes be a physical change (like mixing colored dyes) but is not as definitive as the production of a new substance. The key concept here is that gas production (a new substance) indicates a chemical reaction.

Answer:

D. production of a new substance with new properties