Which compound can exist as stereoisomers?
"D" is the correct answer. 2-Butanol exists as two stereoisomers, R- and S-2-butanol, just as you described.  The "2" carbon in 2-butanol is a chiral carbon atom, it has 4 different groups attached to it (ethyl, methyl, hydroxyl and a hydrogen atom).  The R and S forms of 2-butanol cannot be rotated one into the other, they can only be interconverted by reflecting one in a mirror.  They are non-superimposable mirror images like your right and left hand. Build a model of 2-butanol and then build a second model that is the mirror image of the first - you'll find that you cannot intercovert them by rotation and one is not superimposable upon the other.