Which of the following compounds shows geometrical isomerism `(G.I.)`?
`a.` But`-2-` ene
`b.` `3-` Methyl but `-2-`enoic acid
`c.` `3-` Methyl pent `-2-` enoic acid
`d.` `3-` Phenyl prop `-2-` enoic acid.

Explanation

To determine which of the given compounds shows geometrical isomerism, we need to analyze each compound based on the presence of a double bond and the different substituents attached to the carbon atoms involved in that double bond. Geometrical isomerism (cis/trans or E/Z isomerism) occurs when there are two different groups attached to each carbon of the double bond.

### Step-by-Step Solution:

1. **Analyze But-2-ene (Option a)**:
- Structure: CH₃-CH=CH-CH₃
- The double bond is between the second and third carbon atoms.
- Both carbon atoms involved in the double bond have different substituents (methyl and hydrogen).
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