## **Core Concept**
The structure of an antibody, also known as an immunoglobulin, is crucial for understanding its function in the immune system. Antibodies are Y-shaped proteins composed of two heavy chains and two light chains. Each chain has distinct regions, including variable (V) and constant (C) regions. The variable regions of both the light and heavy chains are responsible for the antibody's specificity and binding to antigens.

## **Why the Correct Answer is Right**
The correct answer indicates that there is 1 variable region on each light chain and 1 variable region on each heavy chain of an antibody. This is accurate because:
- Each light chain has one variable region (VL).
- Each heavy chain has one variable region (VH).
These variable regions come together to form the antigen-binding site, which is unique to each antibody and allows it to bind specifically to one particular antigen.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests a different configuration that does not accurately reflect the structure of antibody chains.
- **Option B:** This option incorrectly states the number of variable regions on either the light or heavy chains.
- **Option C:** This option might suggest multiple variable regions on one chain and none or an incorrect number on the other, which is not accurate.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the specificity of an antibody for its antigen is determined by its variable regions. The combination of VL and VH regions creates a unique binding site for a specific antigen, making this a critical concept in immunology and antibody engineering.

## **Correct Answer:** .