The correct option is C.
Helium is a noble gas and these do not react at all. All noble gases are the most stable elements and can be found in the last column of the periodic table
Every other element here is in column 1. The element in group 1 and 7 are the least stable because they are only 1 electron away from having a full outer shell
The closer an element is to almost having a full outer shell, the more reactive it is
Once it has a full shell (group 8/noble gases) it is stable
