which is indicated if a gas forms when two or more substances are mixed?\na. physical change\nb. chemical…

Brief Explanations:

A chemical change occurs when substances react to form new substances with different chemical properties. The formation of a gas when substances are mixed is a sign of a chemical reaction taking place, which is a chemical change. Physical changes do not result in new substances, and physical properties are characteristics that can be observed without changing the substance's chemical identity. Chemical properties describe a substance's ability to undergo chemical reactions. Since gas - formation indicates a reaction forming a new substance, it's a chemical change.

Answer:

B. chemical change