Molecular weight (mass):
It is the molecular mass of a substance that can be calculated by sum of atomic weight of atoms that are present in the molecule multiple by the total number of molecule.
In KOH,
Atomic weight of K=39.1
Atomic weight of O=15.9
Atomic weight of H=1
Molecular weight=Atomic weight of K+Atomic weight of O+Atomic weight of H
=56.1 g/mol
So the answer is A that is 56.10 g/mol