Under which class of substitution reaction does this reaction appear to fall

This reaction is most likely to fall under SN2 because the thing called carbonication does not occur in SN1. The carbon forms a partial bond with the nucleophile during the intermediate phase and the leaving group. So for this question the reaction will fall under SN2.

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.