Which of the following changes in substances is always considered a physical change?

• A. Rusting of iron
• B. Melting of ice to form liquid water
• C. Decomposition of hydrogen peroxide
• D. Burning of wood

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the difference between physical and chemical changes. A physical change affects the form or state of a substance without changing its chemical composition, while a chemical change results in the formation of new substances with different properties.
2. Step 2: Analyze each option to determine if the chemical composition changes. Rusting of iron involves iron reacting with oxygen to form iron oxide, which is a chemical change.
3. Step 3: Decomposition of hydrogen peroxide breaks it down into water and oxygen, changing its chemical composition, so it is a chemical change.
4. Step 4: Burning of wood involves combustion, producing new substances like carbon dioxide and ash, indicating a chemical change.
5. Step 5: Melting of ice to form liquid water changes the state from solid to liquid but does not alter the chemical composition of H2O, so it is a physical change.