What is the correct order of increasing atomic size among Cu, Mn, Ge, and Sc?

Ge < Cu < Mn < Sc is the increasing order of atomic size.
Cu (29), Mn (25), Ge (32), and Sc (21) belong to the same period of the periodic table (Period 4). 

Moving from left to right in a period, atomic sizes of elements decrease because the effective nuclear charge on the outer shell increases without increasing the number of shells. 

So, Sc which lies on the left-most side of the table has the largest atomic radius while Ge which lies on the right side has the smallest atomic size. 

Hence, the correct order of increasing atomic sizes would be Ge < Cu < Mn < Sc.