It depends on the reactant coefficients as well as the given proportions. first, you have to look at the equation.
4Al + 6HCl -> 3H2 + 2Al2Cl3.
then you have to compare to the given amounts of Al and HCl. you cannot just give the two compounds and ask for the limiting reagent. to save you 5 points, this is how
assume they give you x mols of HCl, y mols of Al.
does 6x>4y or 4y>6x. if 6x>4y, then Aluminium is the limiting reagent. if 6x<4y, HCl is the limiting reagent.