Addition of `OsO_4` to cyclopentene would give a product which is:

Options

A. achiral
B. racemic
C. meso
D. optically active

Explanation

To solve the question regarding the addition of OsO₄ to cyclopentene, we will follow these steps:

### Step 1: Understand the Reaction
Cyclopentene is an alkene, and the addition of OsO₄ (osmium tetroxide) to alkenes typically results in a reaction known as syn-dihydroxylation. This means that two hydroxyl (–OH) groups are added to the double bond in a syn fashion, meaning they are added to the same side of the double bond.

**Hint:** Remember that syn-dihydroxylation results in both substituents being added to the same face of the double bond.

### Step 2: Draw the Structure of Cyclopentene
Cyclopentene is a five-membered ring with one double bond. When you draw it, ensure you represent the double bond correctly.

**Hint:** Visualizing the structure of cyclopentene will help you understand how the addition of OsO₄ occurs.

### Step 3: Perform the Syn-Dihydroxylation
When OsO₄ is added to cyclopentene, it will add two hydroxyl groups across the double bond. Since this addition is syn, both hydroxyl groups will be added to the same side of the cyclopentene ring.

**Hint:** Focus on the geometry of the addition; both hydroxyl groups will be on the same side of the cyclopentene.

### Step 4: Analyze the Product
The product formed from this reaction will be a diol (specifically, a vicinal diol) where both hydroxyl groups are on the same face of the cyclopentane ring. This results in a compound that has a plane of symmetry, making it a meso compound.

**Hint:** Check for symmetry in the product; if it has a plane of symmetry, it is likely a meso compound.

### Step 5: Identify the Correct Option
Given the options provided in the question, the product formed from the reaction of OsO₄ with cyclopentene is indeed a meso compound. Therefore, the correct answer is option three: meso.

**Hint:** When faced with multiple-choice questions, eliminate options that do not fit the characteristics of the product you have identified.

### Final Answer
The addition of OsO₄ to cyclopentene gives a product which is meso.