For each element, give the following information: [1] total number of electrons; [2] group number; [3] number of valence electrons; [4] period; [5] number of the valence shell. a. oxygen b. sodium c. phosphorus

please answer all parts

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16. Average atomic mass is different from mass number because... A. the average atomic mass describes the mass number of a single atom, but mass number describes the average of all exact masses among isotopes of an element. B. mass number describes the approximate mass of the nucleus of a single atom, but average atomic mass describes the weighted average of all the exact masses among isotopes of an element. C. mass number describes the exact mass of a single atom, but average atomic mass describes the average of all mass numbers. O D. mass number describes the approximate mass of the nucleus of a single atom, but average atomic mass describes the largest mass among isotopes of an element.