Which is the limiting reactant when 3.5 g of al and 5.6 g of cl2 react?
The limiting reactant is Cl₂.
You use the usual method for finding limiting reactants.
In your problem, the balanced equation is
2Al + 3Cl₂ → 2AlCl₃
From Al: 3.5 g Al ×
From Cl₂: 5.6 g Cl₂ ×
So the limiting reactant is Cl₂.