Assertion`:-` The dissocation constant of poly basic acid are in order `K_(1)gtK_(2)gtK_(3)`.
Reason`:-` The `H^(+)` ion furnished in first step of dissocation exert common ion effect to reduce the second dissociation and soon.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertiion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are False

Explanation

To solve the question, we need to analyze the assertion and the reason provided regarding the dissociation constants of a polybasic acid.

### Step-by-Step Solution:

1. **Understanding Polybasic Acids**:
- A polybasic acid is an acid that can donate more than one proton (H⁺) per molecule. For example, let’s consider a generic polybasic acid represented as H₃A.

2. **Dissociation Steps**:
- The dissociation of H₃A can be represented in three steps:
- First dissociation:
\[ H_3A \rightleftharpoons H^+ + H_2A^- \]
Here, the dissociation constant is \( K_1 \).
- Second dissociation:
\[ H_2A^- \rightleftharpoons H^+ + HA^{2-} \]
Here, the dissociation constant is \( K_2 \).
- Third dissociation:
\[ HA^{2-} \rightleftharpoons H^+ + A^{3-} \]
Here, the dissociation constant is \( K_3 \).

3. **Analyzing the Dissociation Constants**:
- In the first dissociation, H⁺ ions are produced. The presence of these H⁺ ions will affect the subsequent dissociations due to the common ion effect.
- The common ion effect states that the presence of a common ion (in this case, H⁺) will suppress the dissociation of the acid. Therefore, the more H⁺ ions that are present, the less the second and third dissociations will occur.

4. **Establishing the Order of Dissociation Constants**:
- Since \( K_1 \) represents the first dissociation, it is expected to be the largest because it is not influenced by any other H⁺ ions from prior dissociations.
- For \( K_2 \), it is influenced by the H⁺ ions produced in the first dissociation, leading to a smaller value than \( K_1 \).
- Similarly, \( K_3 \) is influenced by both \( K_1 \) and \( K_2 \), making it the smallest.
- Thus, we have:
\[ K_1 > K_2 > K_3 \]

5. **Conclusion**:
- The assertion that the dissociation constants of a polybasic acid are in the order \( K_1 > K_2 > K_3 \) is correct.
- The reason provided explains that the H⁺ ions from the first dissociation exert a common ion effect that reduces the extent of the second and third dissociations, which is also correct.
- Therefore, both the assertion and reason are true, and the reason correctly explains the assertion.

### Final Answer:
Both the assertion and reason are correct, and the reason is a correct explanation of the assertion.