Which of the following is corred ?

Options

A. All the actinides resemble the lanthanoids quite closely
B. Actinides do not exhibit similarity with lanthanides
C. The second half of the actinides resembles the lanthanides quite closely
D. The first half of the actinides resembles the lanthanides

Explanation

To solve the question "Which of the following is correct?" regarding the similarities between actinoids and lanthanoids, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Series**:
- Actinoids (elements 89 to 103) and lanthanoids (elements 57 to 71) are two series of f-block elements in the periodic table.

2. **Identify Similarities**:
- Both series have similar properties due to their f-orbitals being filled. However, it is important to note that not all actinoids resemble lanthanoids equally.

3. **Examine the Options**:
- **Option A**: "All the actinoids resemble the lanthanoids."
- This is incorrect because only the second half of the actinoids closely resembles the lanthanoids.
- **Option B**: "Actinoids do not exhibit similarity."
- This is also incorrect as there is some similarity, particularly in the second half of the actinoids.
- **Option C**: "Second half of the actinoids resemble the lanthanoids."
- This is correct as the second half of the actinoids shows closer resemblance to the lanthanoids, particularly in their common oxidation state of +3.
- **Option D**: "First half of the actinoids resemble the lanthanoids."
- This is incorrect as the first half does not show significant resemblance.

4. **Conclusion**:
- After analyzing all the options, we find that **Option C** is the correct answer: "Second half of the actinoids resemble the lanthanoids."

### Final Answer:
**Option C**: Second half of the actinoids resemble the lanthanoids.

---