A molecule is said to be chiral if it-

 

Chirality basically means "mirror-image, non-superimposable molecules," and to claim that a molecule is chiral is to say that its mirror image (it must have one) is not the same as it self. A certain collection of overlapping requirements determines whether a molecule is chiral or achiral.

Hence, the correct option (C). cannot be super-imposed on its mirror image.