**Correct Option: B. A substance undergoes a transformation that results in the formation of one or more new substances.** ### Detailed Explanation: To understand why option B is the correct answer, we first need to define what a chemical change is. A chemical change, also known as a chemical reaction, occurs when one or more substances (reactants) are transformed into one or more different substances (products). This transformation involves breaking and forming chemical bonds, which results in a change in the chemical composition of the substances involved. #### Why Option B is Correct: - **Formation of New Substances**: In a chemical change, the original substances undergo a transformation that results in new substances with different properties. For example, when hydrogen gas reacts with oxygen gas to form water, the properties of water are entirely different from those of hydrogen and oxygen. - **Indicators of Chemical Change**: There are often observable signs of a chemical change, such as color change, gas production (bubbles), temperature change (exothermic or endothermic reactions), and the formation of a precipitate (a solid that forms from a solution). These indicators suggest that a new substance has been formed. #### Why the Other Options are Incorrect or Weaker: - **Option A: A substance changes its state from solid to liquid.** - This describes a **physical change**, not a chemical change. In a physical change, the substance may change its state (like melting or freezing), but its chemical composition remains the same. For example, when ice melts to become water, it is still H₂O, just in a different state. - **Option C: A substance is dissolved in a solvent.** - This also describes a **physical change**. When a substance dissolves, such as salt in water, the individual particles separate but do not change their chemical identity. The salt (NaCl) remains NaCl, even though it is in a solution. - **Option D: A substance is mixed with another substance without altering its composition.** - This statement describes a **physical mixture** rather than a chemical change. When two substances are mixed without any chemical reaction occurring, they retain their individual properties and compositions. For example, mixing sand and salt results in a mixture where both components can be separated and retain their original properties. ### Summary of Key Points: - A **chemical change** results in the formation of new substances with different properties. - Indicators of a chemical change include color change, gas production, temperature change, and precipitate formation. - **Physical changes** involve changes in state or mixtures where the original substances retain their chemical identity. ### Revision Summary: - **Chemical Change**: Involves transformation into new substances (correct answer: B). - **Physical Change**: Changes in state or mixtures without altering chemical composition (options A, C, D). - **Indicators of Chemical Change**: Color change, gas production, temperature change, precipitate formation. - **Key Distinction**: Chemical changes alter the chemical identity; physical changes do not.