Assertion: Energy of an isolated particles system is constant.
Reason: Isolated system do not allow exchange of energy

Options

A. a.If both assertion and reason are true and reason is the correct explanation of assertion.
B. b. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. c. If assertion is true but reason is false.
D. d. If both assertion and reason are false.

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step 1: Understand the Assertion
The assertion states that "Energy of an isolated particle system is constant."

- An isolated system is defined as a system that does not interact with its surroundings. This means that there is no exchange of energy or matter with the environment.

### Step 2: Understand the Reason
The reason states that "Isolated systems do not allow exchange of energy."

- This statement is true. In an isolated system, since there is no interaction with the surroundings, there can be no transfer of energy into or out of the system.

### Step 3: Connect Assertion and Reason
Now, we need to connect the assertion and the reason:

- Since an isolated system does not allow the exchange of energy, the total energy within the system remains constant over time. This is consistent with the law of conservation of energy, which states that energy cannot be created or destroyed in an isolated system.

### Step 4: Conclusion
Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the correct option is that the reason is the correct explanation for the assertion.

### Final Answer
The correct option is **A**: Both the assertion and reason are true, and the reason is the correct explanation for the assertion.

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