Select correct statement (s):

Options

A. Across a transition series (from `Cr` to `Cu)`, there is only a small change in atomic radius from one element to another due to very small change in effective nuclear charge.
B. The rate of decrease in the size across the lanthanide series is less than the across the first transition series.
C. Both are correct statements
D. None of the statement is correct.

Explanation

To solve the question, we need to analyze the given statements and determine their correctness based on our understanding of periodic trends, particularly in transition metals and lanthanides.

### Step-by-Step Solution:

1. **Understanding the First Statement:**
- The first statement discusses the atomic radius of transition metals from chromium to copper.
- It mentions that there is only a small change in atomic radius due to a small change in effective nuclear charge.
- As we move across a transition series, the addition of d-electrons occurs, which does not significantly increase the shielding effect on the outermost electrons (4s electrons).
- Therefore, the atomic radius does not change much from chromium to copper. This statement is **correct**.

2. **Understanding the Second Statement:**
- The second statement compares the rate of decrease in atomic size across the lanthanide series to that across the first transition series.
- It states that the decrease in size across the lanthanide series is less than that across the first transition series.
- This phenomenon is attributed to lanthanide contraction, where the addition of f-electrons leads to poor shielding of the nuclear charge, resulting in a smaller atomic size.
- Hence, this statement is also **correct**.

3. **Conclusion:**
- Since both statements A and B are correct, the answer to the question is option C: both statements are correct.

### Final Answer:
Both statements A and B are correct. Therefore, the answer is option C.

---