Question

which of the following best describes why some elements are more chemically reactive than others?
○ chemical reactivity depends on how radioactive the element is. elements at the bottom of the periodic table are extremely radioactive.
○ chemical reactivity depends on what periodic table class the element is in. nonmetals, like chlorine, are much more reactive than metals, like zinc.
○ chemical reactivity depends on the arrangement of an atoms electrons. different elements have different numbers of valence electrons.
○ chemical reactivity depends on the mass of the nucleus of an atom. the heavier the element is, the more unstable the atom is.

Explanation:

• Option 1: Radioactivity is not the main factor for chemical reactivity. Radioactive elements' instability is nuclear, not directly about chemical reactions. So this is incorrect.
• Option 2: Reactivity isn't determined by being a metal or non - metal in a general "class - based" way. For example, some metals (like alkali metals) are very reactive, and some non - metals are less reactive. So this is wrong.
• Option 3: Chemical reactivity is related to the arrangement of electrons, especially valence electrons. Atoms react to achieve a stable electron configuration (like a full outer shell), and the number of valence electrons determines how easily an atom can gain, lose, or share electrons. This is correct.
• Option 4: The mass of the nucleus (related to atomic mass) doesn't determine chemical reactivity. Chemical reactions involve electrons, not the nucleus (except in nuclear reactions). So this is incorrect.

Answer:

The option "Chemical reactivity depends on the arrangement of an atom's electrons. Different elements have different numbers of valence electrons." (the third option with the blue dot)