a. Arrange the following species in decreasing order of their sizes//ionic radii.
i. `Ar, K^(o+),Cl^(ɵ),S^(2-)` and `Ca^(2+)`

Explanation

To arrange the species `Ar`, `K^(+1)`, `Cl^(-1)`, `S^(2-)`, and `Ca^(2+)` in decreasing order of their sizes (ionic radii), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Species and Their Charges:**
- We have the following species:
- Argon (Ar) - neutral atom
- Potassium ion (K^(+1)) - cation
...