I am still a first year student; I was asked in the exam to identify the meso comound out of some choices. The answer key said that the compound below is meso. But I see no plane of symmetry here. Am I wrong or the question? I hope someone clarifies please. Sorry if the question was super silly.
As the comments imply, having a center of symmetry makes a molecule achiral. This is because, geometrically, inverting through the center equals a mirror reflection plus a 180° rotation. If you start with an atom at point $(x,y,z)$ and you reflect it through the $xy$ plane, the atom is now at $(x,y,-z)$. Now rotate 180° around the $z$ axis and you're at $(-x,-y,-z)$ just like inverting through the center.
Your molecule has no symmetry with respect to just a mirror reflection or just a 180° rotation. (It might look like you could rotate 180° within the plane of the paper, but the stereochemistry is different.) But it does have a symmetry with respect to the combination of the two, which is that center of inversion, so you can match the mirror image to the original by allowing the rotation. That makes the molecule meso.