What determines how reactive an element is?

• A. Its atomic radius
• B. Its willingness to share electrons
• C. Its melting point
• D. Its color

Answer: (B)

Reactivity comes from how easily atoms adjust their electrons to form bonds and reach a stable arrangement. The ability to share electrons directly reflects bonding tendencies, so an element that is willing to share electrons tends to bond readily with others, showing higher reactivity in many contexts. Metals often react by losing electrons, while nonmetals react by gaining or sharing them, but the common thread is how readily electrons are involved in forming bonds.

The other properties—atomic radius, melting point, and color—describe size, how a substance melts, and how it appears, respectively, but they don’t determine how readily an element reacts with other substances.