The correct answer is A. halogen.
Halogens are elements in the periodic table that have seven valence electrons. They are highly reactive and form salts with metals. The halogens are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
Transitive elements are elements in the periodic table that are in the d-block. They are characterized by having partially filled d-orbitals. The transitive elements are found in groups 3-12 of the periodic table.
Inert gases are elements in the periodic table that have a full valence shell of electrons. They are very stable and do not react with other elements. The inert gases are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).
Differential transitive elements are elements in the periodic table that have a valence shell of electrons that is not completely filled. They are found in groups 3-12 of the periodic table.