Compound `(A)`, an alkene with molecule formula `(C_(5)H_(10))` exists in various strictures. On mononcholorination and dichlorination, it again shows various structures and streoisomers.
Which isomer of `(A)` shows styereoisomerism ?

Options

A.
B.
C.
D.

Explanation

To solve the problem, we need to identify which isomer of compound (A), an alkene with the molecular formula C5H10, exhibits stereoisomerism. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the molecular formula
The molecular formula C5H10 indicates that compound (A) is an alkene, which means it contains at least one carbon-carbon double bond. Alkenes can have different structural isomers based on the arrangement of their carbon atoms and the position of the double bond.

**Hint:** Remember that alkenes can have structural isomers due to the presence of double bonds.

### Step 2: Identify possible isomers
For C5H10, we can draw various structural isomers. Some common isomers include:
1. 1-pentene
2. 2-pentene (which can exist as cis and trans)
3. cyclopentene
4. methylcyclobutane
5. 3-methyl-1-butene, etc.

**Hint:** Consider both linear and cyclic structures when identifying isomers.

### Step 3: Analyze stereoisomerism
Stereoisomerism can be of two types:
- Geometric (cis-trans) isomerism
- Optical isomerism (chiral centers)

For geometric isomerism to occur, there must be restricted rotation around the double bond, and different groups must be attached to the carbons involved in the double bond.

**Hint:** Look for double bonds where different substituents are attached to the carbons involved in the double bond.

### Step 4: Identify isomers with potential for stereoisomerism
Among the isomers, 2-pentene is notable because it has a double bond between the second and third carbon atoms. It can exist as:
- **Cis-2-pentene**: where the two methyl groups are on the same side of the double bond.
- **Trans-2-pentene**: where the two methyl groups are on opposite sides of the double bond.

Both forms exhibit geometric isomerism.

**Hint:** Check for the presence of different groups on either side of the double bond to confirm geometric isomerism.

### Step 5: Check for optical isomerism
For optical isomerism, we need to find a chiral center (a carbon atom attached to four different groups). In the case of trans-2-pentene, it does not have a chiral center, but it can still exhibit geometric isomerism.

However, if we consider other isomers like certain substituted cyclopentanes, we may find chiral centers.

**Hint:** Look for carbon atoms bonded to four different substituents to identify chiral centers.

### Conclusion
The isomer of compound (A) that shows stereoisomerism is **2-pentene**, which can exist as both cis and trans forms. Therefore, the answer to the question is:

**Answer:** Option (B) - 2-pentene shows stereoisomerism.