Final answer:
The term 'Axis of mirror' is not standard and does not belong in the group that includes line of reflection, mirror line, and axis of symmetry, which are all synonymous terms used in the context of symmetry and reflection in geometry and optics.
Step-by-step explanation:
The item that does not belong to the group is D) Axis of mirror because the other three terms are commonly used to describe elements related to symmetry and reflection in geometry and optics, where line of reflection, mirror line, and axis of symmetry are synonymous. They represent a line where an object can be folded or reflected over to produce two identical halves. The term 'Axis of mirror' is not a standard term in this context. Additionally, in the study of optics, the optical axis is a key concept where rays that are parallel to it reflect through the focal point in a spherical mirror.