Mesotartaric acid is optically inactive due to the presence of:

Options

A. Geometrical isomerism
B. Two chiral carbon atoms
C. Molecular symmetry
D. External compensation

Explanation

To determine why mesotartaric acid is optically inactive, we can follow these steps:

### Step 1: Understand the Structure of Mesotartaric Acid
Mesotartaric acid is a type of tartaric acid that has two chiral centers. However, it is classified as a meso compound.

**Hint:** Look for the structural features that define meso compounds, particularly the presence of chiral centers and symmetry.

### Step 2: Identify Chiral Centers
In mesotartaric acid, there are two chiral carbon atoms. Each chiral center can create a non-superimposable mirror image, which typically leads to optical activity.

**Hint:** Remember that chiral centers contribute to optical activity, but other factors can influence the overall optical behavior of the molecule.

### Step 3: Recognize the Concept of Optical Inactivity
Despite having chiral centers, mesotartaric acid is optically inactive. This is due to the presence of a plane of symmetry in its molecular structure.

**Hint:** Think about how symmetry can affect the optical activity of a compound. A plane of symmetry can lead to internal compensation.

### Step 4: Understand Molecular Symmetry
The presence of a plane of symmetry means that one half of the molecule is a mirror image of the other half. This results in the optical activities of the two halves canceling each other out.

**Hint:** Consider how the arrangement of atoms in the molecule can lead to a balance that negates optical activity.

### Step 5: Conclusion
Thus, mesotartaric acid is optically inactive due to molecular symmetry, specifically the presence of a plane of symmetry that leads to internal compensation.

**Final Answer:** Mesotartaric acid is optically inactive due to the presence of molecular symmetry.