Which of the following is represent in a chemical change?

Options

A. Remain constant in temperature
B. Change in colour
C. Evolution of a gas
D. Both b and c

Explanation

To determine which of the following represents a chemical change, we need to understand the characteristics of a chemical change. A chemical change is typically defined by the following features:

1. **Irreversibility**: Once a chemical change occurs, it cannot be easily reversed to return to the original state.
2. **Formation of new substances**: A chemical change results in the formation of one or more new substances with different properties.
3. **Change in color**: A noticeable change in color often indicates that a chemical reaction has occurred.
4. **Evolution of gas**: The production of gas during a reaction is another sign of a chemical change.
5. **Change in temperature**: Chemical reactions can be exothermic (release heat) or endothermic (absorb heat), leading to a change in temperature.

Now, let's analyze the options provided:

1. **Option 1: Remain constant in temperature** - This does not represent a chemical change. Chemical reactions often involve changes in temperature.

2. **Option 2: Change in color** - This is a characteristic of a chemical change. If the color changes, it indicates that new substances may have formed.

3. **Option 3: Evolution of a gas** - The production of gas is also a characteristic of a chemical change. If gas is evolved, it suggests that a reaction has taken place.

4. **Option 4: Both B and C** - Since both the change in color and the evolution of gas are characteristics of chemical changes, this option is correct.

### Conclusion:
The correct answer is **Option 4: Both B and C** represent a chemical change.

---