Answer:
The equilibrium law
Explanation:
According to the equilibrium law , when 
of any of the reactants or the products in the reaction at an equilibrium state, is changed, then it changes the composition of equilibrium mixture in order to minimize the effect of
Acetic acid (in excess) + 
⇄ 
+ water
is a reaction which involves the equilibrium. So to force the reaction towards the side of , one of the reactant is taken in excess. All this can be explained easily by applying the equilibrium law.
Answer: Cu
Explanation: It is Cu because the origin of the word Copper comes from the latin word "Cuprum".
The volume stays the same
