The correct answer is C. halogen.
Elements in group 17 of the periodic table are called halogens. They are highly reactive and form salts with metals. The halogens are fluorine, chlorine, bromine, iodine, and astatine.
Alkaline metals are elements in group 1 of the periodic table. They are very reactive and form strong bases. The alkaline metals are lithium, sodium, potassium, rubidium, cesium, and francium.
Alkaline earth metals are elements in group 2 of the periodic table. They are less reactive than the alkaline metals but still form strong bases. The alkaline earth metals are beryllium, magnesium, calcium, strontium, barium, and radium.
Inert gases are elements in group 18 of the periodic table. They are very stable and do not react with other elements. The inert gases are helium, neon, argon, krypton, xenon, and radon.