Which of the following is not a chemical reaction?

Options

A. Burning of coal
B. Purification of milk
C. Vaporisation
D. Formation of water

Explanation

To determine which of the following options is not a chemical reaction, we need to analyze each option provided:

1. **Burning of Coal**: This is a combustion reaction where coal reacts with oxygen to produce carbon monoxide, carbon dioxide, heat, and light. The composition of the reactants changes to form different products. Therefore, this is a chemical reaction.

2. **Purification of Milk**: This process often involves removing impurities or altering the composition of milk through methods like pasteurization or filtration. These methods change the characteristics and composition of the milk, making it a chemical reaction.

3. **Vaporization**: This process involves changing a substance from a liquid to a gas (or vapor) state by heating. Importantly, the chemical composition of the substance remains unchanged during this phase transition. Therefore, vaporization is not a chemical reaction; it is a physical change.

4. **Formation of Water**: This is a chemical reaction that occurs when hydrogen gas reacts with oxygen gas to form water. The reactants are transformed into a new product with a different chemical composition. Thus, this is a chemical reaction.

Based on the analysis, the option that is not a chemical reaction is:

**Vaporization**.