Ba(OH)₂(aq) + 2HNO₃(aq) = Ba(NO₃)₂(aq) + 2H₂O(l)
At the reaction of barium hydroxide with nitric acid there are no visual changes.
Ba(OH)₂(aq) + H₂SO₄(aq) = BaSO₄(s) + 2H₂O
At the reaction of barium hydroxide with sulfuric acid the precipitat of white color is formed.
        
             
        
        
        
4 is correct. Since gases are made of rapidly moving molecules with a relatively high amount of kinetic energy, the molecules have a hard time coming together to form a liquid. You must lower their kinetic energy with a low temperature and force the molecules together with high pressure.
        
                    
             
        
        
        
Stoich questions...
1) convert the grams of Au to moles
(33.5g)/(196.7g/mol)=___x___
2)find how many atoms are in that many moles by multiplying it by avogadro's number.
x(moles of Au)*(6.02*10^23)=?
3)now that you have found the number of atoms of gold, convert it to grams of aluminum by multiplying it by Avogadro's number and multiplying it by the atomic mass of aluminum.
( ? )(6.02*10^23)(26.98g/mol)= (mass of Al)