Question

1. elements on the periodic table of elements are primarily listed in a particular order. they are arranged by -

common physical states

the number of protons

reactivity

metallic qualities

Explanation:

The modern periodic table organizes elements based on their atomic number, which is equal to the number of protons in an atom's nucleus. This arrangement ensures elements with similar properties fall into the same groups and periods, unlike organizing by physical state, reactivity, or metallic qualities which do not follow a consistent, systematic order for all elements.

Answer:

the number of protons