Final answer:
Bromine is the element that is a halogen, as it belongs to Group 17, commonly known for forming salts with metals.
Step-by-step explanation:
The element from the provided options that is a halogen is bromine (Br). Group 17, also known as the halogens, includes fluorine, chlorine, bromine, iodine, and astatine. Bromine is well-known for its reactions with metals to form compounds such as sodium bromide and potassium bromide.
Lithium, mentioned in the question, is not a halogen but an alkali metal which belongs to Group 1. Argon, another element from the options provided, is a noble gas located in Group 18. Calcium and lithium are not halogens, as calcium is an alkaline earth metal in Group 2, and lithium, as previously mentioned, is an alkali metal in Group 1.