Which of the following is a physical change?

• A. Milk sours when left out of the refrigerator
• B. Tums (containing CaCO₃) neutralizes stomach acid.
• C. Sugar caramelizing when heated on a skillet.
• D. Tearing a piece of paper.

Answer: (D)

Verified step by step guidance

1. Understand the difference between physical and chemical changes. A physical change involves a change in physical properties without altering the chemical composition, while a chemical change results in the formation of new substances.
2. Examine the first option: 'Milk sours when left out of the refrigerator.' This involves a chemical change because the milk undergoes fermentation, producing lactic acid and changing its chemical composition.
3. Consider the second option: 'Tums (containing CaCO3) neutralizes stomach acid.' This is a chemical change as it involves a reaction between calcium carbonate and hydrochloric acid in the stomach, forming new substances like carbon dioxide and water.
4. Look at the third option: 'Sugar caramelizing when heated on a skillet.' This is a chemical change because heating sugar causes it to break down and form new compounds, changing its chemical structure.
5. Finally, evaluate the fourth option: 'Tearing a piece of paper.' This is a physical change because tearing paper changes its shape and size but does not alter its chemical composition.