An optically active compound, having molecular formula `C_6 H_12 O_6` is found in two isomeric forms. When isomers dissolved in water, they show the following equilibria
`underset(alpha=111^(n))("[A]") hArr underset(52.5^@)("equilibrium mixture") hArr underset(19.2)("[B]")`
Such isomers are called

Options

A. Anomers
B. Enantiomers
C. Positional isomers
D. Geometrical isomers

Answer

To solve the problem, we need to analyze the information provided about the optically active compound with the molecular formula \( C_6H_{12}O_6 \) and its isomeric forms.

### Step-by-Step Solution:

1. **Identify the Compound**: The molecular formula \( C_6H_{12}O_6 \) corresponds to a carbohydrate, specifically a hexose sugar. The most common hexose sugars are glucose, fructose, and galactose.

2. **Determine the Isomeric Forms**: The problem states that there are two isomeric forms of the compound. Given the context of carbohydrates, these isomers are likely to be different anomers of glucose, which are alpha (α) and beta (β) forms.

3. **Understand Optical Activity**: The optical activity of a compound refers to its ability to rotate plane-polarized light. The degree of rotation is given for each form:
- Compound A has a rotation of \( +111^\circ \) (α-D-glucose).
- The equilibrium mixture has a rotation of \( +52.5^\circ \).
- Compound B has a rotation of \( +19.2^\circ \) (β-D-glucose).

4. **Establish the Equilibrium**: The equilibrium between the two forms indicates that when dissolved in water, α-D-glucose and β-D-glucose can interconvert. The equilibrium mixture's rotation indicates the presence of both forms in a specific ratio.

5. **Identify the Type of Isomers**: The isomers in question, α-D-glucose and β-D-glucose, differ only in the configuration around the anomeric carbon (C1). Therefore, they are classified as anomers.

6. **Conclusion**: The isomers are called **anomers**. Anomers are a type of stereoisomer that differ at the anomeric carbon, which is the carbon that becomes a new chiral center when a sugar cyclizes.

### Final Answer:
The isomers are called **anomers**.