The correct answer is A.
A chiral molecule is one that is not superimposable on its mirror image. A racemic mixture is a mixture of equal amounts of two enantiomers, which are mirror images of each other that are not superimposable. A meso compound is a chiral molecule that is superimposable on its mirror image.
In option A, the molecule is a meso compound. It has two chiral centers, but the two chiral centers are mirror images of each other. Therefore, the molecule is superimposable on its mirror image and is optically inactive.
In option B, the molecule has two chiral centers, but the two chiral centers are not mirror images of each other. Therefore, the molecule is not superimposable on its mirror image and is optically active.
In option C, the molecule has one chiral center. A molecule with one chiral center can be either optically active or optically inactive. In this case, the molecule is optically inactive because the chiral center is a plane of symmetry. A plane of symmetry is a plane that divides a molecule into two mirror image halves.
In option D, the molecule has no chiral centers. Therefore, the molecule is not optically active.