Which of the following gases has the greatest density at STP? a) H2 b) Ar c) He O d) F2 O e e) Cl2 Question 15 (Mandatory) (2 points) Aluminum metal reacts with HCl to produce aluminum chloride and hydrogen gas. 2Al(s) + 6HCl(aq) 2AlCl3(aq) + 3H2(g) How many grams of aluminum metal must be added to an excess of HCl to produce 16.8 L of hydrogen gas? Assume STP conditions. a) 20.28 b) 6.78 c) 121.41 8 d) 13.5 g e) 33.78