A physical change is a type of change that occurs in the physical properties of a substance, such as size, shape, state, or phase, without altering its chemical composition. Therefore, to determine which option is a physical change, we need to consider whether the process described involves a change in the physical properties of the substance or not.
- Freezing ice cream: This involves a change in state from liquid to solid without changing the chemical composition of the ice cream, so it is a physical change.
- Dissolving calcium in water: This is a process that involves a chemical change since it results in the formation of calcium ions and hydroxide ions in the water.
- Burning kerosene: This is a chemical change since it involves the combustion of kerosene to produce carbon dioxide and water vapor.
- Exposing white phosphorus to air: This is a chemical change since it involves the reaction of white phosphorus with oxygen in the air to form a new substance, phosphorus oxide.
Therefore, the only option that describes a physical change is "Freezing ice cream".