Concrete a mixture or pure substance?

Cement is a mixture.

Explanation: It is composed of different types of compound particles. Each of the components of concrete by themselves would be pure substances. For example, a sample of just calcium oxide would be a pure substance because the particles in the sample would all be identical calcium oxide compounds.

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.