Tartaric acid `[HO_(2)CCH(OH)CH(OH)CO_(2)H]` was an important compound in history of stereochemistry.
Two naturally occuring forms of tartaric acid are optically inactive. One optically inactive form (P) has a melting point of 210-`212^(@)`C and can be separated into two optically acitve forms, whereas other optically inactive form (Q) cannot be resolved further.
Optically inactive form Q is

Options

A.
B.
C.
D. none of these

Answer

To determine the optically inactive form Q of tartaric acid from the given options, we need to analyze the molecular structures based on their symmetry and superimposability. Here’s a step-by-step solution:

### Step 1: Understand the Concept of Optical Activity
Optical activity refers to the ability of a compound to rotate plane-polarized light. A compound is optically inactive if it does not rotate light, which typically occurs in achiral compounds or racemic mixtures.

**Hint:** Remember that for a compound to be optically inactive, it must either be achiral or a racemic mixture.

### Step 2: Identify the Given Structures
We are given three structures of tartaric acid (let's call them A, B, and C). We need to analyze each structure to determine if they are superimposable mirror images.

**Hint:** Focus on the symmetry of the structures and look for any elements that would make them non-superimposable.

### Step 3: Analyze Structure A
In structure A, we observe the following:
- The arrangement of functional groups is such that when we attempt to create a mirror image, the positions of the hydroxyl (OH) and hydrogen (H) atoms do not match up perfectly.
- Therefore, structure A is not superimposable and is optically active.

**Hint:** Check if the mirror image of the structure can be aligned perfectly with the original structure.

### Step 4: Analyze Structure B
In structure B, we find:
- The two halves of the molecule are identical when we create a mirror image. The positions of the functional groups (COOH, OH, and H) are symmetrical.
- This means that structure B is superimposable on its mirror image and is thus optically inactive.

**Hint:** Look for symmetry in the arrangement of atoms and functional groups.

### Step 5: Analyze Structure C
For structure C, we see:
- Similar to structure A, the arrangement of the functional groups does not allow for superimposition. The positions of the hydroxyl (OH) and hydrogen (H) atoms differ on either side.
- Therefore, structure C is also optically active.

**Hint:** Compare the arrangement of atoms in structure C with its mirror image to see if they align.

### Conclusion
Based on the analysis, the only structure that is optically inactive (superimposable on its mirror image) is **Structure B**. Therefore, the optically inactive form Q of tartaric acid is:

**Answer:** Structure B