Chemistry: The Central Science (13th Edition)

124$u$
The molecular mass of $KMnO_4$ can be found as follows: Making the sum of the multiplication of the atomic mass of each by the element by the quantity of atoms of the element in the substance. As shown below. MM ($KMnO_4$) = $(1\times39)+(1\times24)+(4\times16)= 124u$