Assertion : In the formation of a molecule , only the outer shell electrons take part in chemical combination and they are known as valence electrons.
Reason : Atoms achieve the stable octet when they are linked by chemical bonds .

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 in 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 assertion-reason question, we will analyze both the assertion and the reason step by step.

### Step 1: Analyze the Assertion
The assertion states: "In the formation of a molecule, only the outer shell electrons take part in chemical combination and they are known as valence electrons."

- **Explanation**: This statement is true. Valence electrons are indeed the electrons present in the outermost shell of an atom. These electrons are responsible for chemical bonding because they determine how an atom can interact with other atoms. For example, in sodium (Na), which has an electronic configuration of 2, 8, 1, the single electron in the outermost shell is the valence electron that participates in bonding.

### Step 2: Analyze the Reason
The reason states: "Atoms achieve the stable octet when they are linked by chemical bonds."

- **Explanation**: This statement is also true. Atoms tend to achieve a stable electronic configuration, often referred to as an octet, which is typically 8 electrons in their outer shell. Atoms can achieve this stable configuration by gaining, losing, or sharing electrons through chemical bonds. For instance, sodium can lose its one valence electron to achieve a stable configuration similar to neon (Ne), which has a complete octet.

### Step 3: Determine the Relationship
Now we need to determine if the reason provided is a correct explanation of the assertion.

- **Analysis**: While both statements are true, the reason does not specifically explain why only the outer shell electrons (valence electrons) are involved in bonding. The reason discusses the stable octet but does not clarify the role of valence electrons in the bonding process.

### Conclusion
Both the assertion and reason are true, but the reason is not the correct explanation for the assertion. Therefore, the correct option is that both the assertion and reason are true, but the reason is not the correct explanation of the assertion.

### Final Answer
Both the assertion and reason are true, but the reason is not the correct explanation of the assertion.

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