The___ of an element is the number of element.*
__ of an atom of that
atomic mass, electrons in the nucleus
mass number, neutrons in the nucleus
mass number, protons plus neutrons in the outermost energy level
atomic number, protons in the nucleus

atomic mass, neutrons in the nucleus

Explanation: because I remember from when I took honors chemistry last year we learned about this and it’s called the atomic mass when looking at an atom and the neutrons in the nucleus are effected by it.

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-