Which of the following is not a part of compound microscope ?

A compound microscope is an optical instrument used to magnify small objects. Its structural and optical components include:

• Mirror: Used to reflect external light through the diaphragm to illuminate the specimen.
• Stage: The flat platform where the slide containing the specimen is placed for observation.
• Clip: Metal or plastic brackets on the stage that hold the glass slide firmly in place.

In contrast, the Retina is a biological component of the human eye. It is the light-sensitive innermost layer of the eyeball where images are formed and converted into nerve impulses. Since the retina is an anatomical part of an organism and not a mechanical or optical part of a microscope, Option D is the correct answer.