To balance the chemical equation, we need to make sure that the number of atoms of each element on both sides of the equation is equal. The balanced equation is:Fe + 6HCl FeCl3 + 3H2Now, we can determine how many moles of hydrogen gas H2 will be formed when 0.25 moles of Fe react with an excess of HCl. According to the balanced equation, 1 mole of Fe reacts to produce 3 moles of H2. So, we can set up a proportion:1 mole Fe / 3 moles H2 = 0.25 moles Fe / x moles H2Solving for x:x moles H2 = 0.25 moles Fe * 3 moles H2 / 1 mole Fex moles H2 = 0.75 moles H2Therefore, 0.75 moles of hydrogen gas will be formed when 0.25 moles of Fe react with an excess of HCl.