Which of the following is a lanthanide ?

Options

A. Curium
B. Californium
C. Uranium
D. Europium

Explanation

To determine which of the given options is a lanthanide, we need to analyze the electronic configurations and atomic numbers of the elements provided. Here's a step-by-step solution:

### Step 1: Understand the Definition of Lanthanides
Lanthanides are a series of 15 chemical elements with atomic numbers from 57 (Lanthanum) to 71 (Lutetium). They are characterized by the filling of the 4f subshell and have a general electronic configuration of \( [Xe] 4f^{1-14} 5d^{0-1} 6s^2 \).

### Step 2: Analyze the Given Options
We will evaluate the electronic configuration and atomic number of each option provided.

1. **Curium (Cm)**
- Atomic Number: 96
- Electronic Configuration: \( [Rn] 5f^7 6d^1 7s^2 \)
- Conclusion: Curium is an actinide.

2. **Californium (Cf)**
- Atomic Number: 98
- Electronic Configuration: \( [Rn] 5f^{10} 6d^0 7s^2 \)
- Conclusion: Californium is also an actinide.

3. **Uranium (U)**
- Atomic Number: 92
- Electronic Configuration: \( [Rn] 5f^3 6d^1 7s^2 \)
- Conclusion: Uranium is an actinide.

4. **Europium (Eu)**
- Atomic Number: 63
- Electronic Configuration: \( [Xe] 4f^7 5d^0 6s^2 \)
- Conclusion: Europium is a lanthanide.

### Step 3: Identify the Lanthanide
From the analysis, we can conclude that:
- Curium, Californium, and Uranium are all actinides.
- Europium is the only element that fits the criteria of a lanthanide.

### Final Answer
**Europium (Eu)** is the lanthanide among the given options.

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