Which group of elements includes fluorine, chlorine, bromine, and iodine?

The group of elements that includes fluorine, chlorine, bromine, and iodine is known as the halogens. Halogens are located in Group 17 of the periodic table and are characterized by having seven valence electrons, which makes them very reactive as they tend to gain an electron to achieve a full outer shell. This reactivity is evident in their ability to form salts when they react with metals, hence the name "halogen," which comes from the Greek words for "salt-former."

The halogens also exhibit distinct molecular forms; for instance, fluorine and chlorine exist as diatomic molecules (F₂ and Cl₂) at room temperature, while bromine is a liquid and iodine is a solid under standard conditions. Each of these elements has unique properties and uses, contributing to their significance in both chemistry and various industrial applications.

In contrast, other groups mentioned in the other choices, such as noble gases, lanthanides, and transition metals, consist of very different types of elements with different properties and typical behaviors. Noble gases, for example, are known for their lack of reactivity due to having a complete valence shell, while lanthanides and transition metals have complex electron configurations and are primarily found in the f-block