A graph shows how the temperature of a substance changes as energy is added steadily over time. Which part of the graph would indicate a phase change is taking place?

a flat, horizontal line

a steep, upward sloping line

a steep, downward sloping line

the answer would be a

i think it's letter a.

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.