Consider the following chemical reaction at equilibrium.
H2SO4(aq)
2H+(aq) + SO42-(aq)
The addition of which compound will cause a shift in equilibrium because of a common ion effect?
O Naci
O KNO3
0 MgSO4
O FeCl2

answer by yourhope:

how do models compare to real-world objects?

d. most models represent a real-world object in a simpler way.

: )

  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-

the answer would be a