Assertion:The whole mass of the atom is concentrated in the nucleus.
Reason:The whole mass of the atom is concentrated in the nucleus
Reason:The mass of a nucleus can be either less than or more than the sum of the masses of nucleons present in it.

Options

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

Explanation

To solve the question, we will analyze the assertion and reason step by step.

### Step 1: Analyze the Assertion
The assertion states: "The whole mass of the atom is concentrated in the nucleus."

- **Explanation**: This statement is true. Most of the mass of an atom is indeed concentrated in the nucleus, which is made up of protons and neutrons (collectively known as nucleons). Electrons, which orbit the nucleus, contribute very little to the overall mass of the atom.

### Step 2: Analyze the Reason
The reason states: "The mass of a nucleus can be either less than or more than the sum of the masses of nucleons present in it."

- **Explanation**: This statement is incorrect. The mass of the nucleus is always less than the sum of the individual masses of the nucleons. This discrepancy arises due to the binding energy, which is the energy that holds the nucleons together. According to Einstein's mass-energy equivalence principle (E=mc²), some mass is converted into binding energy, resulting in a lower mass for the nucleus compared to the sum of the individual nucleons.

### Step 3: Conclusion
- The assertion is true, but the reason is false. Therefore, the correct option is that the assertion is true, but the reason is false.

### Final Answer
The correct option is **C**: Assertion is true, but reason is false.

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