Among isomeric butenes, ......... .. is the most stable.

Explanation

To determine which isomeric butene is the most stable, we will analyze the structures and stability of the different butene isomers: but-1-ene, cis-2-butene, and trans-2-butene.

### Step-by-Step Solution:

1. **Identify the Isomers of Butene**:
- But-1-ene: CH2=CH-CH2-CH3
- Cis-2-butene: CH3-CH=CH-CH3 (with both methyl groups on the same side)
- Trans-2-butene: CH3-CH=CH-CH3 (with methyl groups on opposite sides)
...