The `E`-isomer among the following is:

Options

A.
B.
C.
D.

Explanation

To determine which isomer is the `E`-isomer among the given compounds, we need to follow these steps:

### Step-by-Step Solution:

1. **Understand E/Z Isomerism**:
- E/Z isomerism occurs in alkenes where there is restricted rotation around a double bond. The `E` (from the German "entgegen") isomer has the higher priority groups on opposite sides of the double bond, while the `Z` (from "zusammen") isomer has them on the same side.

2. **Identify the Double Bond**:
- Look at the compounds provided and identify the double bonds (C=C).

3. **Assign Priorities**:
- For each substituent attached to the double bond, assign priority based on the Cahn-Ingold-Prelog priority rules. The atom with the higher atomic number gets higher priority. If the first atoms are the same, look at the next atoms in the substituent chains until a difference is found.

4. **Analyze Each Compound**:
- **Compound A**:
- Identify groups: C=C, Br, C2H5, Cl, C3H7.
- Assign priorities: Br > C2H5 and Cl > C3H7.
- Both higher priority groups are on the same side → Z configuration.
- **Compound B**:
- Identify groups: C=C, C2H5, CHO (aldehyde), Cl, C3H7.
- Assign priorities: CHO > C2H5 and Cl > C3H7.
- Higher priority groups are on opposite sides → E configuration.
- **Compound C**:
- Identify groups: C=C, C2H5, C3H7, H.
- Assign priorities: C3H7 > H and C3H7 > H.
- Both higher priority groups are on the same side → Z configuration.
- **Compound D**:
- Identify groups: C=C, CH, Cl2, CH, Cl2, H, C3H7.
- Assign priorities: Cl2 > CH and Cl2 > H.
- Both higher priority groups are on the same side → Z configuration.

5. **Conclusion**:
- After analyzing all compounds, only **Compound B** has the E configuration because the higher priority groups are on opposite sides of the double bond.

### Final Answer:
The `E`-isomer among the given compounds is **Compound B**.

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