Which answer choices best indicate that a substance has experienced a chemical change?

• when the substance changes forms

• when a new substance is formed

• when the substance changes shape

• when the substance changes volume

The best answer choices that indicate a substance has experienced a chemical change are:

• when a new substance is formed

• when the substance changes forms

The best answer choice that indicates a substance has experienced a chemical change is:

• when a new substance is formed

The answer choices that best indicate that a substance has experienced a chemical change are:

- When a new substance is formed: In a chemical change, the identity of the substance changes, resulting in the formation of one or more new substances with different chemical properties.

- When the substance changes forms: While changes in physical form, such as from solid to liquid or gas, can occur in both physical and chemical changes, this answer choice by itself is not a strong indicator of a chemical change.

- When the substance changes shape: Changes in shape typically indicate a physical change, where the arrangement or orientation of the substance's particles is altered without a change in its chemical properties.

- When the substance changes volume: Changes in volume usually point towards a change in physical properties such as compression or expansion, rather than a chemical change where the substance's chemical composition is altered.

So, the answer choice "when a new substance is formed" is the most accurate and reliable indication that a substance has experienced a chemical change.