For keyboard navigation, use the up/down arrow keys to select an answer. a) Because the positive charge is on primary and secondary allylic carbocations etc. b) Because the positive charge is on a primary and a tertiary carbon c) Because the positive charge is on a primary and a secondary carbon d) Because the positive charge is on a secondary and a tertiary carbon

b) because the positive charge is on primary and a tertiary carbon

Explanation:

The allylic carbon atom carries positive charge when primary carbon has positive charge. It forms an ion with tertiary carbon atom to form resonance. In secondary carbocation the positive charge is on secondary carbon atom. The atom are attracted and electrons form carbon -  carbon sigma.

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.