Which of the following actions would cause a physical change in a substance?

• A. Rusting of iron to form Fe_2O_3
• B. Burning wood to produce ash and gases
• C. Melting ice to form liquid water
• D. Reacting vinegar with baking soda to produce CO_2 gas

Answer: (C)

Verified step by step guidance

1. Understand the difference between physical and chemical changes: A physical change affects the form or state of a substance without changing its chemical identity, while a chemical change results in the formation of new substances with different chemical properties.
2. Analyze the rusting of iron: Rusting involves iron reacting with oxygen to form iron oxide (Fe_2O_3), which is a new substance, so this is a chemical change.
3. Analyze burning wood: Burning wood produces ash, gases, and heat, indicating a chemical reaction where new substances are formed, so this is a chemical change.
4. Analyze melting ice: Melting ice changes water from solid to liquid state, but the chemical composition (H_2O) remains the same, so this is a physical change.
5. Analyze reacting vinegar with baking soda: This reaction produces carbon dioxide gas and other products, indicating a chemical change because new substances are formed.