The decreasing tendency to exist in puckered 8 - membered ring structure is 

Options

A. `S gt Se gt Te gt Po`
B. `Se gt S gt Te gt Po`
C. `S gt Te gt Se gt Po`
D. `Te gt Se gt S gt Po`

Answer

To determine the decreasing tendency of elements to exist in a puckered 8-membered ring structure, we need to consider the elements from Group 16 of the periodic table: sulfur (S), selenium (Se), tellurium (Te), and polonium (Po).

### Step-by-Step Solution:

1. **Identify the Elements**: The elements we are considering are sulfur (S), selenium (Se), tellurium (Te), and polonium (Po). These elements belong to Group 16 of the periodic table.

2. **Understand Ring Structures**: An 8-membered ring structure is a cyclic compound consisting of eight atoms. The ability of an element to form such a structure depends on its size and the nature of its bonding.

3. **Consider Atomic Size**: Smaller atoms are generally more favorable for forming stable ring structures due to less steric hindrance and better orbital overlap. As we move down the group from sulfur to polonium, the atomic size increases.

4. **Evaluate Each Element**:
- **Sulfur (S)**: Being the smallest, sulfur can easily form an 8-membered ring due to its suitable size and bonding capabilities.
- **Selenium (Se)**: Larger than sulfur but still capable of forming an 8-membered ring, though less favorably than sulfur.
- **Tellurium (Te)**: Larger than selenium, making it less favorable for forming stable ring structures.
- **Polonium (Po)**: The largest of the group, polonium is the least likely to form an 8-membered ring due to its size and instability.

5. **Establish the Decreasing Order**: Based on the above evaluations, the decreasing tendency to exist in a puckered 8-membered ring structure is:
- Sulfur (S) > Selenium (Se) > Tellurium (Te) > Polonium (Po)

### Final Answer:
The decreasing tendency to exist in puckered 8-membered ring structure is:
**Sulfur > Selenium > Tellurium > Polonium**