The odd item amongst the following is C. Light pen.
A computer mouse is a pointing device that detects two-dimensional motion relative to a surface. It is typically used to control the cursor on a computer screen, and can also be used to select items on the screen and to enter text.
A touchpad is a pointing device that is typically used on laptops. It is a flat surface that can be used to move the cursor on a computer screen by dragging your finger across the surface.
A printer is a device that prints text or images onto paper.
A light pen is a pointing device that is used to interact with a computer screen. It works by detecting light that is reflected from the screen. Light pens are not commonly used today, as they have been replaced by other pointing devices such as the mouse and the touchpad.