Based on formal charge considerations, the electron dot structures of CO3 2- ion has A) two resonance structures involving two single bonds and one double bond.
B) two resonance structures involving one single bond and two double bonds.
C) three resonance structures involving two single bonds and one double bond.
D) three resonances structures involving one single bond and two double bonds.

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.