Answer:
C
Explanation:
The reason is that C represents group 17 of the periodic table, the halogens.
The halogens are a group of elements (in group 17) that are one electron short from achieving their full octet, and being stable. Due to this fact, they are extremely reactive, and will react with almost any substance to accept that one extra electron to become stable.
The other groups represented by letters are:
A- Alkali metals
B- Alkaline metals
C- Halogens
D- Nobel gasses
