Flexion is a movement, which occurs in________plane.

The correct option is Sagittal.

To understand why flexion occurs in the sagittal plane, it is helpful to look at how anatomical planes divide the human body and how movements are defined within them:
1. The Sagittal Plane: This vertical plane passes through the body from front to back, dividing it into right and left halves. Movements that occur in this plane involve forward and backward motions.
2. Defining Flexion: Flexion is an anatomical movement that decreases the angle between two body parts or bones at a joint (such as bending the elbow or knee). Because this bending motion occurs in a forward-or-backward direction, it takes place parallel to the sagittal plane.
3. Comparison with Other Planes:
- The Frontal (or Coronal) plane divides the body into front and back portions; movements in this plane are side-to-side, such as abduction and adduction.
- The Transverse (or Horizontal) plane divides the body into upper and lower portions; movements in this plane involve rotation.

Therefore, flexion is a movement that occurs specifically in the sagittal plane.