Screening effect is not observed in :

Options

A. `He^(+)`
B. `Li^(2+)`
C. `Be^(3+)`
D. In all cases

Explanation

To solve the question about the screening effect not being observed in He+, Li2+, or Be3+, we will analyze the concept of the screening effect and how it applies to these ions.

### Step-by-Step Solution:

1. **Understand the Screening Effect**:
- The screening effect refers to the phenomenon where inner electrons in an atom shield outer electrons from the full effect of the nuclear charge. This occurs because the inner electrons repel the outer electrons, reducing the effective nuclear charge felt by the outer electrons.

2. **Identify the Ions**:
- We have three ions to consider: He+ (Helium ion), Li2+ (Lithium ion), and Be3+ (Beryllium ion).
- Each of these ions has lost electrons: He+ has 1 electron, Li2+ has 1 electron, and Be3+ has 1 electron.

3. **Determine the Electron Configuration**:
- He+ has 1 electron (1s).
- Li2+ has 1 electron (1s).
- Be3+ has 1 electron (1s).
- In all these cases, there is only one electron remaining after ionization.

4. **Analyze the Screening Effect**:
- For the screening effect to be significant, there should be multiple electrons present in the inner shells to effectively shield the outer electrons from the nuclear charge.
- Since all three ions have only one electron, there are no inner electrons to provide any shielding. Therefore, the screening effect is not observed.

5. **Conclusion**:
- Since all three ions (He+, Li2+, Be3+) have only one electron, the screening effect is not observed in any of these cases. Thus, the correct answer is that screening effect is not observed in all of the given options.

### Final Answer:
The screening effect is not observed in: **He+, Li2+, and Be3+** (all of them).

---