Which is the correct order of ionic sizes (At. No. : Ce=58, Sn=50, Yb=70 and Lu=71)

Options

A. `CegtSngtYbgtLu`
B. `SngtCegtLugtYb`
C. `LugtYbgtSngtCe`
D. `SngtYbgtCegtLu`

Explanation

To determine the correct order of ionic sizes for the elements Cerium (Ce), Tin (Sn), Ytterbium (Yb), and Lutetium (Lu), we need to consider a few key concepts regarding ionic sizes and periodic trends.

### Step-by-Step Solution:

1. **Identify the Elements and Their Groups:**
- Cerium (Ce) - Atomic Number 58 (f-block element)
- Tin (Sn) - Atomic Number 50 (p-block element)
- Ytterbium (Yb) - Atomic Number 70 (f-block element)
- Lutetium (Lu) - Atomic Number 71 (f-block element)

2. **Understand the Concept of Ionic Size:**
- Ionic size refers to the radius of an ion. Cations (positively charged ions) are generally smaller than their parent atoms due to the loss of electrons, while anions (negatively charged ions) are larger due to the gain of electrons.

3. **Consider the Lanthanide Contraction:**
- The lanthanide contraction refers to the phenomenon where the ionic radii of the lanthanide elements decrease with increasing atomic number. This occurs because the f-electrons do not shield the nuclear charge effectively, leading to a stronger attraction between the nucleus and the outer electrons.

4. **Order the Elements Based on Their Ionic Sizes:**
- **Cerium (Ce)**: Being the first in the series of f-block elements, it has a relatively larger ionic size compared to the others.
- **Tin (Sn)**: As a p-block element, it is smaller than Ce but larger than Yb and Lu due to the lanthanide contraction.
- **Ytterbium (Yb)**: As a later f-block element, it is smaller than Ce and Sn because of the increased nuclear charge and the effects of lanthanide contraction.
- **Lutetium (Lu)**: Being the last in the series of f-block elements, it has the smallest ionic size due to the maximum nuclear charge and the effects of lanthanide contraction.

5. **Final Order of Ionic Sizes:**
- Based on the above analysis, the correct order of ionic sizes from largest to smallest is:
- Ce > Sn > Yb > Lu

### Conclusion:
The correct order of ionic sizes is:
**Ce > Sn > Yb > Lu**