Arrange the following elements in decreasing order of their radii:
(A) La
(B) Pr
(C) Gd
(D) Yb
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (B), (C), (D)
Arrange the elements in decreasing order of atomic radii: La, Pr, Gd, Yb.
Step 1: Consider periodic trends
- All these elements are lanthanides.
- Across the lanthanide series (La → Yb), the atomic/ionic radius decreases due to lanthanide contraction.
Step 2: Identify the order
- La (atomic number 57) → largest radius
- Pr (59) → slightly smaller than La
- Gd (64) → smaller than Pr
- Yb (70) → smallest
Step 3: Arrange in decreasing order
$\text{La} > \text{Pr} > \text{Gd} > \text{Yb}$