Which of the following changes is not a physical change?

Options

A. glowing of filament in bulb
B. combustion
C. boiling of water
D. sublimation

Answer

To determine which of the following changes is not a physical change, we first need to understand the definition of a physical change. A physical change is a change that affects one or more physical properties of a substance without altering its chemical composition. In other words, during a physical change, the substance may change its state (like solid, liquid, gas) or appearance, but no new substances are formed, and the change is usually reversible.

### Step-by-Step Solution:

1. **Identify the Options**:
- Look at the list of changes provided in the question. You need to analyze each one to determine whether it is a physical change or a chemical change.

2. **Understanding Physical Changes**:
- Physical changes include processes such as melting, freezing, boiling, condensation, and sublimation. These changes are characterized by the fact that they do not produce new substances.

3. **Analyze Each Change**:
- **Glowing of Filament in Bulbs**: This is a physical change. The filament (usually made of tungsten) heats up and glows when electricity passes through it, but it does not change chemically.
- **Combustion Reactions**: This is a chemical change. When a substance (like a hydrocarbon) combusts, it reacts with oxygen to form new products (like CO2 and water).
- **Boiling of Water**: This is a physical change. Water changes from liquid to gas, but it remains H2O.
- **Sublimation**: This is also a physical change. A solid changes directly to gas without becoming liquid (e.g., dry ice).

4. **Conclusion**:
- From the analysis, the change that is not a physical change is the **combustion reaction**. This is because it involves the formation of new chemical products, which makes it a chemical change.

### Final Answer:
The change that is not a physical change is **combustion reactions**.