Question

A corona around the moon is seen when we view it on a foggy or misty night. This is due to

Answer 1

In meteorology, a corona (plural coronae) is an optical phenomenon produced by the diffraction of sunlight or moonlight (or, occasionally, bright starlight or planetlight) by individual small water droplets and sometimes tiny ice crystals of a cloud or on a foggy glass surface.

since fog  has water molecule in it that's why in the foggy and  misty nights a corona is seen around the moon.