A device in which a chain reaction is initiated and controlled with the purpose of producing electrical power is called ?

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.

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.