A molecule is chiral if it is non-superimposable on its mirror image — this is the fundamental definition of chirality. The presence of a chiral center (a carbon bearing four different substituents) is the most common cause, but not the only one. Option (A) is wrong: a plane of symmetry makes a molecule achiral. Option (C) is wrong: rotating light to the left makes it levorotatory (–), but chirality doesn't require any specific direction of rotation.