La (lanthanum) having atomic number 57 is a member of :

Options

A. s-block elements
B. p-block elements
C. d-block elements
D. f-block elements

Answer

To determine the classification of lanthanum (La) with atomic number 57, we can follow these steps:

### Step 1: Identify the Atomic Number
- The atomic number of lanthanum is 57. This means it has 57 protons and, in a neutral atom, 57 electrons.

### Step 2: Write the Electronic Configuration
- The electronic configuration of lanthanum can be determined by filling the orbitals according to the Aufbau principle.
- The configuration is:
- 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s².
- This can be simplified using the noble gas notation:
- [Xe] 6s².

### Step 3: Determine the Last Electron Shell
- The last filled subshell in the electronic configuration is 6s². However, we also need to consider the next subshell that will be filled, which is the 5d subshell.

### Step 4: Identify the Block
- Lanthanum is classified based on the subshell that contains the last electron that will be filled.
- Since the last electron enters the 5d subshell after the 6s subshell is filled, lanthanum is classified as a d-block element.

### Step 5: Conclusion
- Therefore, lanthanum (La) is a member of the d-block elements.

### Final Answer
- Lanthanum (La) is a member of the d-block elements.

---