Water is a pure substance. Which of the following is true about water? Its compounds can only be chemically separated into the elements that make it up.
Its compounds can only be physically separated into the elements that make it up.
It is made up of a variety of compounds, each with a different set of properties.
It is made up of one element and one compound, each with the same properties.

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.