A friend says that only mirrors and other shiny surface reflects light. Explain what is wrong with this reasoning?
Mirrors and other shiny surfaces reflect the exact image received, but almost all surfaces reflect some light
Mirrors reflect light in such a way that we see a reverse image of whatever is in front of the mirror. Because of this, we say the image in the mirror is a "reflection" (in the mathematical sense) of the original image.
While mirrors and other shiny surfaces are the only surfaces that mathematically reflect the images received, this does not mean that they are the only surfaces that reflect light.
Think about it this way: in order for us to see anything at all, some light has to hit our eyes. But, not everything emits light directly. In order for us to see the world around us, it has to take light emitted from a source (such as the sun) and reflect it in such a way that we see some of that light.
Of course, not all objects are "smart" enough to reflect the exact image they receive. Most objects simply absorb some colors of light and reflect others. For example, grass is green because it absorbs all colors of light from the sun except for green light (and a few other pigments which aren't as noticeable).
Hopefully this makes sense and helps you understand that, while non-shiny objects don't produce a mathematical reflection of their surroundings, they are visible, and therefore still do reflect light.