(A): Elements of second and third transition series have nearly same atomic radii
(R): Lanthanide contraction is observed in the elements from atomic number 58 to 71. 

Options

A. Both A & R are true, R is the correct explanation of A
B. Both A & R are true, R is not correct explanation of A
C. A is true, R is false
D. A is false, R is true

Answer

To solve the question, we need to analyze the statements (A) and (R) provided:

**Statement (A):** Elements of second and third transition series have nearly the same atomic radii.
**Statement (R):** Lanthanide contraction is observed in the elements from atomic number 58 to 71.

### Step-by-Step Solution:

1. **Understanding Lanthanide Contraction:**
- The lanthanide series consists of elements with atomic numbers from 58 (Cerium) to 71 (Lutetium).
- The lanthanide contraction refers to the phenomenon where the atomic and ionic radii of the lanthanide elements decrease with increasing atomic number, despite the addition of electrons. This is due to poor shielding of the f-electrons, resulting in a higher effective nuclear charge.

**Hint:** Remember that lanthanide contraction is a result of poor shielding by f-electrons, leading to a stronger attraction between the nucleus and the outermost electrons.

2. **Impact on Atomic Radii of Transition Series:**
- The second transition series (3d series) includes elements from Scandium (Sc) to Zinc (Zn), and the third transition series (4d series) includes elements from Yttrium (Y) to Cadmium (Cd).
- When moving from the second to the third transition series, one would typically expect an increase in atomic radii due to the addition of a new electron shell. However, the lanthanide contraction affects the atomic radii of the elements in the third transition series (4d).

**Hint:** Compare the expected trend of increasing atomic radii with the actual trend influenced by lanthanide contraction.

3. **Conclusion on Statements (A) and (R):**
- Due to the lanthanide contraction, the atomic radii of the third transition series elements are not significantly larger than those of the second transition series elements. Thus, they have nearly the same atomic radii.
- Therefore, both statements (A) and (R) are true, and (R) provides a correct explanation for (A).

**Hint:** Assess whether the explanation (R) logically supports the claim made in (A).

### Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A).