Which of the following will not be able to show optical isomerism (enantiomerism)?

Options

A. `1,2`-Propadiene
B. `2,3`-Pentadiene
C. sec-Butyl alcohol
D. All exhibit enantiomerism

Explanation

To determine which of the given compounds will not be able to show optical isomerism (enantiomerism), we will analyze each option step by step.

### Step 1: Analyze 1,2-Propadiene
1,2-Propadiene has the structure:
\[ \text{CH}_2=\text{C}=\text{CH}_2 \]
In this molecule, the terminal carbon atoms each have two hydrogen atoms attached. Therefore, there is a plane of symmetry present in the molecule. Since it contains a plane of symmetry, it cannot show optical isomerism.

### Step 2: Analyze 2,3-Pentadiene
2,3-Pentadiene has the structure:
\[ \text{CH}_3-\text{CH}=\text{C}=\text{CH}-\text{CH}_3 \]
In this structure, the second and third carbon atoms have different groups attached (one has a hydrogen and the other has a methyl group). There is no plane of symmetry present in this molecule, which allows it to show optical isomerism.

### Step 3: Analyze Secondary Butyl Alcohol
Secondary butyl alcohol has the structure:
\[ \text{CH}_3-\text{CH(OH)}-\text{CH}_2-\text{CH}_3 \]
The second carbon (the one with the hydroxyl group) is a chiral center because it is attached to four different groups (methyl, hydroxyl, hydrogen, and ethyl). Therefore, this compound can show optical isomerism.

### Conclusion
From the analysis:
- 1,2-Propadiene **cannot** show optical isomerism due to the presence of a plane of symmetry.
- 2,3-Pentadiene **can** show optical isomerism.
- Secondary butyl alcohol **can** show optical isomerism.

Thus, the compound that will not be able to show optical isomerism is **1,2-Propadiene**.

### Final Answer
The correct answer is **Option 1: 1,2-Propadiene**.

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