Which of the following is most likely a physical change?

• A. Rusting of iron (Fe) when exposed to air
• B. Burning of methane (CH_4) in oxygen
• C. Decomposition of hydrogen peroxide (H_2O_2) into water and oxygen
• D. Melting of ice to form liquid water

Answer: (D)

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 each option to determine if it involves a chemical reaction or just a change in physical state:
3. Rusting of iron (Fe) involves iron reacting with oxygen to form iron oxide, which is a chemical change because new substances are formed.
4. Burning of methane (CH_4) in oxygen is a combustion reaction producing carbon dioxide and water, indicating a chemical change.
5. Decomposition of hydrogen peroxide (H_2O_2) into water and oxygen involves breaking chemical bonds and forming new substances, so it is a chemical change.
6. Melting of ice to form liquid water involves a change in state from solid to liquid without altering the chemical composition of H_2O, making it a physical change.