Electronic configuration of elements of interest are as follows:
1) Kr = [Ar] 3d10 4s2 4p6
2) Rb = [Kr] 5s1
3) Si = [Ne] 3s2 3p2
4) Mg = [Ne] 3s2
5) Br = [Ar] 3d10 4s2 4p5
From above listed electronic configurations of different elements, it can be seen that expect Kr, all the elements has partially filled atomic orbitals. Hence, they will be reactive in nature. So, Kr is likely to be chemically nonreactive.
