Assertion (A): The equivalent mass of element is varialbe.
Reason (R ): It depents on the valency of the element.

Options

A. If both (A) and (R ) are correct and (R ) is the correct explantion for (A)
B. If both (A) and (R ) are correct but (R ) is not the correct explantion for (A)
C. If (A) is correct but (R ) is incorrect.
D. If (A) and (R ) are incorrect.

Explanation

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

### Step 1: Understand the Assertion
The assertion states that "The equivalent mass of an element is variable."
- **Explanation**: This means that the equivalent mass of an element can change depending on certain conditions or factors.

### Step 2: Understand the Reason
The reason states that "It depends on the valency of the element."
- **Explanation**: The valency of an element refers to its ability to combine with other elements, which directly affects its equivalent mass. The equivalent mass is calculated using the formula:
\[ \text{Equivalent Mass} = \frac{\text{Atomic Mass}}{\text{n}} \]
where \( n \) is the valency of the element.

### Step 3: Analyze the Relationship
- If the valency (n) of an element changes, the equivalent mass will also change. For example, if an element has a valency of 1 in one reaction and a valency of 2 in another, its equivalent mass will be different in each case.

### Step 4: Conclusion
Both the assertion and the reason are correct. The assertion is true because the equivalent mass is variable, and the reason is also true because it explains why the equivalent mass varies—it depends on the valency of the element.

### Final Answer
Both the assertion (A) and the reason (R) are correct, and the reason (R) is the correct explanation of the assertion (A).

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