Which of the following molecule is not chiral 

Chiral compounds: A molecule is chiral if it is not superimposable on its mirror image. most chiral molecules can be identified by their lack of plane of symmetry (or) a center of symmetry.  (or)

To show chirality, a compound should have at least an asymmetric carbon i.e., carbon having different substituents on it.

So option B is not a chiral due to two same  substituents  are attached to carbon atom.