A: Oxalates and carbonates of lanthanides are almost insoluble in water
R: Salts of lanthanides usually contains water of crystallisation

Options

A. (1) Assertion is true, Reason is true, Reason is a correct explanation for Assertion
B. (2) Assertion is true, Reason is true, Reason is not a correct explanation for Assertion.
C. (3) Assertion is true, Reason is false
D. (4) Both assertion and Reason are false.

Explanation

To determine the relationship between the assertion and reason provided in the question, we can break down the information step by step.

### Step 1: Understanding the Assertion
The assertion states that "Oxalates and carbonates of lanthanides are almost insoluble in water."

- **Explanation**: Lanthanides, which are elements from cerium (Ce) to lutetium (Lu), tend to form compounds that are not soluble in water, particularly their oxalates and carbonates. This is due to their larger ionic sizes and the nature of the bonds formed in these compounds.

### Step 2: Understanding the Reason
The reason given is "Salts of lanthanides usually contain water of crystallization."

- **Explanation**: Many lanthanide salts, including their oxalates and carbonates, incorporate water molecules into their crystal structure, which is referred to as water of crystallization. This water can affect the solubility of the salts in water.

### Step 3: Analyzing the Relationship
Now we need to analyze if the reason correctly explains the assertion.

- The assertion is true as lanthanide oxalates and carbonates are indeed mostly insoluble in water.
- The reason is also true; lanthanide salts often contain water of crystallization.
- The presence of water of crystallization can contribute to the overall stability of the solid and its insolubility in water.

### Conclusion
Both the assertion and reason are correct, and the reason provides a correct explanation for the assertion.

### Final Answer:
Assertion (A) and Reason (R) are both correct, and R is the correct explanation of A.

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