Which particle may be gained, lost, or shared by an atom when it forms a chemical bond?

protons

neutrons

electrons

nucleons

Electrons because the amount of valence electrons determines the bonds it can form and often times during a chemical bond or the forming of a compound an element will lose some of its electrons.

the answer to your question is c.

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  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-