Which of the following statements regarding d block elements are true?

Options

A. the colour of anhydrous `CuSO_(4)` is blue
B. "spitting of silver" can be prevented by covering the surface of molten silver with charcoal
C. Iodine liberated in a reaction can ber estimated by titration against a standard thiosulphate solution
D. Lanthanium is first element of third transition series

Answer

To determine which statements regarding d-block elements are true, let's analyze each statement step by step.

### Step 1: Analyze Statement 1
**Statement**: The color of anhydrous copper sulfate is blue.

**Analysis**:
- Copper sulfate (CuSO₄) in its hydrated form (CuSO₄·5H₂O) is indeed blue due to the presence of water molecules.
- However, when copper sulfate is in its anhydrous form (CuSO₄), it appears white.

**Conclusion**: This statement is **incorrect**.

### Step 2: Analyze Statement 2
**Statement**: Spitting of silver can be prevented by covering the surface of molten silver with charcoal.

**Analysis**:
- Spitting of silver refers to the phenomenon where molten silver absorbs oxygen, which can lead to the scattering of silver particles upon cooling.
- It is true that the spitting can be controlled by adding a deoxidant like charcoal to the molten silver, which prevents oxygen absorption.

**Conclusion**: This statement is **correct**.

### Step 3: Analyze Statement 3
**Statement**: Iodine liberated in a reaction can be estimated by titration against a standard thiosulfate solution.

**Analysis**:
- In iodometry, liberated iodine can indeed be titrated against sodium thiosulfate (Na₂S₂O₃), which is a reducing agent.
- However, the statement implies that the concentration of iodine itself is being directly determined, which is misleading. The titration helps in determining the concentration of thiosulfate, not iodine directly.

**Conclusion**: This statement is **incorrect**.

### Step 4: Analyze Statement 4
**Statement**: Lanthanum is the first element of a third transition series.

**Analysis**:
- In the modern periodic table, lanthanum (La) is indeed considered the first element of the third transition series (elements 57 to 71, which includes the lanthanides).

**Conclusion**: This statement is **correct**.

### Final Summary
- **Correct Statements**:
- Statement 2: Spitting of silver can be prevented by covering the surface of molten silver with charcoal.
- Statement 4: Lanthanum is the first element of a third transition series.

- **Incorrect Statements**:
- Statement 1: The color of anhydrous copper sulfate is blue.
- Statement 3: Iodine liberated in a reaction can be estimated by titration against a standard thiosulfate solution.