The correct answer is A. Electron affinity.
Electron affinity is a measure of the tendency of an atom or molecule to attract an electron to form a negative ion. It is defined as the energy released when an electron is added to a neutral atom or molecule in the gas phase to form a negative ion.
Halogens are elements in the periodic table that have a high electron affinity. This means that they are very good at attracting electrons. When an electron is added to a halogen atom, it forms a negative ion with a stable electron configuration. This is why halogens are often used in reactions where they need to react with other elements to form compounds.
Electronegativity is a measure of the ability of an atom to attract electrons to itself. It is defined as the ability of an atom in a chemical bond to attract electrons towards itself.
Electrochemicals are substances that undergo chemical reactions when an electric current is passed through them.
Electropositivity is a measure of the tendency of an atom to lose electrons. It is defined as the ability of an atom to lose electrons and form a positive ion.