Reflection of light is a fundamental property of all mirrors. bill and bett wanted to produce a virtual image using one of the mirrors supplied by their teacher. to do this, they should choose a mirror.

In a plane mirror the image formed is virtual because it is a copy of the real object. It looks as if the object is behind the mirror and not in front of it or on the surface, but it is not really there. However, it can be seen when we focus it with our eyes.  

In addition, the image is symmetrical, because apparently it is at the same distance from the mirror; of  the same size as the object and upright, because it retains the same orientation as the object.

its c its is a mixture of gases

no. dot product   =0 when vecs at right angles