Which of the following elements is a halogen?

Bromine is classified as a halogen, which is a group of elements found in Group 17 of the periodic table. Halogens are known for their reactivity, particularly with alkali metals and alkaline earth metals to form various salts. Bromine is unique among the halogens as it is a liquid at room temperature, unlike the other halogens, which are gases or solids at room temperature.

The other elements mentioned have distinct classifications and properties. Aluminum is a post-transition metal, calcium belongs to the alkaline earth metals, and gold is classified as a transition metal. These elements do not exhibit the same reactivity and properties associated with halogens, emphasizing the unique characteristics of bromine within its group. Understanding the periodic table and the classification of elements is crucial for identifying halogens and recognizing their behaviors in chemical reactions.