Question

a chemical change-- a can easily be reversed by physical means. b alters a substance’s chemical structure to create a new substance. c alters a substance’s physical appearance to create a new substance. d alters a substance’s observable properties.

Explanation:

To solve this, we analyze each option:

• Option A: Chemical changes are not easily reversed by physical means (physical changes are often reversible by physical means), so A is incorrect.
• Option B: A chemical change involves a change in the chemical structure of a substance, resulting in the formation of a new substance. This matches the definition of a chemical change.
• Option C: Altering physical appearance (like shape, state) is a physical change, not a chemical change (which involves chemical structure), so C is incorrect.
• Option D: Altering observable properties can be a physical change (e.g., melting changes state, an observable property, but is physical). Chemical changes do more than just alter observable properties—they create new substances, so D is incorrect.

Answer:

B. alters a substance’s chemical structure to create a new substance