In chemistry, reactivity describes what?

• A. The density of an element
• B. The tendency of elements to react with other substances
• C. The melting point of an element
• D. The color of an element

Answer: (B)

Reactivity is the tendency of an element or compound to react with other substances. This describes how readily it undergoes chemical change, such as forming bonds or transferring electrons, under given conditions. The ease of these processes is tied to electronic structure: valence electrons, ionization energy, and electron affinity (or electronegativity) determine whether an atom is inclined to lose or gain electrons. For metals, lower ionization energy means electrons are lost more easily, leading to higher reactivity; for nonmetals, a strong drive to gain electrons also boosts reactivity. Physical properties like density, melting point, or color tell us about appearance and state, not how readily a substance reacts.