Assertion (A) : On cooling in a freezing mixture, colout of the mixture turns to pink from deep blue for a reaction.
`underset(("Pink"))(Co(H_(2)O)_(6)^(2+))(aq)+4CI^(Theta)hArr underset((Blue))(CoCI_(4)^(2-)(aq))+6H_(2)O(l)`
Reason (R) : The reaction is endothermic in forward reaction,so on cooling the reaction, deep blue colour appears.

Options

A. If both (A) and (R) are correc, and (R) is the correct explanation of (A).
B. If both (A) and (R) are correct but (R) is not the correct explanation of (A).
C. If (A) is correct, but (R) is incorrect.
D. If (A) is incorrect, but (R) is correct.

Explanation

To solve the assertion and reasoning question, we will analyze both the assertion (A) and the reason (R) provided in the question step by step.

### Step 1: Understanding the Assertion (A)
The assertion states that on cooling in a freezing mixture, the color of the mixture changes from deep blue to pink. The reaction given is:
\[ \text{Co(H}_2\text{O)}_6^{2+}(aq) + 4\text{Cl}^- \rightleftharpoons \text{CoCl}_4^{2-}(aq) + 6\text{H}_2\text{O}(l) \]

In this reaction, the cobalt complex changes from an octahedral form (pink) to a tetrahedral form (blue) when chloride ions are added. Therefore, when the temperature is lowered, the equilibrium shifts back to the left, resulting in the formation of the pink complex.

### Step 2: Understanding the Reason (R)
The reason states that the reaction is endothermic in the forward direction, so on cooling, the deep blue color appears.

However, in an endothermic reaction, lowering the temperature shifts the equilibrium towards the reactants (the left side of the equation) according to Le Chatelier's principle. This means that the pink color (from the reactants) would be favored as the temperature decreases, not the blue color.

### Step 3: Evaluating the Assertion and Reason
- **Assertion (A)**: True. The color does change from deep blue to pink upon cooling.
- **Reason (R)**: True, but it does not correctly explain the assertion. The reason given is misleading because it suggests that cooling would favor the deep blue color, while in fact, it favors the pink color.

### Conclusion
Both the assertion and the reason are true, but the reason does not provide the correct explanation for the assertion. Therefore, the correct option for this question is B.

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

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