Amongst the following compounds, the optically active alkane having lowest molecular mass is:

Options

A. `CH_(3)-CH_(2)-CH_(3)`
B.
C. `CH_(3)-CH_(2)-overset(CH_(3))overset(|)(CH)-CH_(3)`
D. `CH_(3)-CH_(2)-C-=C-H`

Explanation

To determine which of the given compounds is the optically active alkane with the lowest molecular mass, we will analyze each compound step by step.

### Step 1: Identify the Compounds
Let's denote the compounds as A, B, C, and D for clarity. We need to check each compound for chirality and molecular mass.

### Step 2: Analyze Compound A
- **Structure**: Compound A has two identical groups attached to a carbon atom.
- **Chirality**: Since it has two identical groups, it cannot be chiral (optically inactive).
- **Conclusion**: Compound A is not optically active.

### Step 3: Analyze Compound B
- **Structure**: Compound B has a carbon atom bonded to four different groups: a cyclopentane ring, an ethyl group (C2H5), a methyl group (CH3), and a hydrogen atom (H).
- **Chirality**: Since all four groups attached to the chiral carbon are different, this compound is chiral and therefore optically active.
- **Molecular Mass**: Calculate the molecular mass of Compound B. (Assuming the molecular formula is CxHy, calculate based on the specific structure provided).

### Step 4: Analyze Compound C
- **Structure**: Compound C has one hydrogen atom, two methyl groups (CH3), and one other group attached to a carbon atom.
- **Chirality**: Since there are two identical methyl groups, this compound cannot be chiral (optically inactive).
- **Conclusion**: Compound C is not optically active.

### Step 5: Analyze Compound D
- **Structure**: Compound D has a carbon atom with a hydrogen atom, a methyl group (CH3), and a carbon chain with a triple bond.
- **Chirality**: The presence of identical groups (two CH3 groups) means it cannot be chiral.
- **Conclusion**: Compound D is not optically active.

### Step 6: Compare Molecular Masses
- Now, we need to compare the molecular masses of the compounds we analyzed:
- Compound A: Not optically active.
- Compound B: Optically active (calculate its molar mass).
- Compound C: Not optically active.
- Compound D: Not optically active.

### Final Conclusion
- The only optically active compound is Compound B, and it has the lowest molecular mass among the options provided.

### Answer
The optically active alkane having the lowest molecular mass is **Compound B**.

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