Which statement describes a physical change?

Which statement describes a physical change?

• A. Dissolving salt in water
• B. Rusting iron
• C. Burning wood
• D. Cooking an egg

Answer: (A)

Physical changes involve a change in form or phase without making a new substance. Dissolving salt in water fits this because the salt disperses and becomes ions in solution, but it remains the same chemical species and the process is reversible by evaporating the water, so no new substance is formed. In contrast, rusting iron, burning wood, and cooking an egg all involve chemical changes where new substances with different properties are produced (iron oxide, ash and gases, denatured and coagulated proteins), which are not simply reversible through physical means.

Physical changes involve a change in form or phase without making a new substance. Dissolving salt in water fits this because the salt disperses and becomes ions in solution, but it remains the same chemical species and the process is reversible by evaporating the water, so no new substance is formed. In contrast, rusting iron, burning wood, and cooking an egg all involve chemical changes where new substances with different properties are produced (iron oxide, ash and gases, denatured and coagulated proteins), which are not simply reversible through physical means.