Two substances were combined and immediately a gas was produced. What type of change is occurring?

• A. A physical change
• B. A nuclear change
• C. A phase change
• D. A chemical change

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the definitions of the types of changes: A physical change involves changes in state or appearance without altering the chemical composition; a nuclear change involves changes in the nucleus of atoms; a phase change is a type of physical change involving changes between solid, liquid, and gas states; a chemical change involves the formation of new substances with different properties.
2. Step 2: Analyze the problem statement: Two substances are combined and immediately a gas is produced. The production of a gas suggests a new substance is formed, which is a key indicator of a chemical change.
3. Step 3: Recognize that physical changes and phase changes do not produce new substances, they only change the form or state of the original substances.
4. Step 4: Understand that nuclear changes involve changes in atomic nuclei, which is not indicated here since the problem involves common substances reacting to produce gas.
5. Step 5: Conclude that since a new substance (gas) is produced from the combination of two substances, the change is a chemical change.