Which of the following describes a physical test for water?

• A. It boils at 100°C
• B. It turns pink with blue cobalt chloride paper
• C. Anhydrous copper sulfate turns blue
• D. It conducts electricity strongly

Answer: (A)

Using a physical property to identify water. Water’s boiling point at standard atmospheric pressure is 100°C, so heating a liquid and observing boiling at 100°C is a direct indication that the sample behaves like water under those conditions. This is a physical test because it relies on a phase change with no chemical reaction occurring. The other options involve changes that come from chemical interactions with water or depend on impurities: cobalt chloride or copper sulfate tests rely on hydration reactions that alter the compound, and conductivity depends on dissolved ions, which is not unique to water.