Answer: 121.7558 amu
Explanation:
Average atomic mass of the unknown element =
(Mass of isotope 1 x Relative Abundance of Isotope 1) + ( Mass of Isotope 2 x Relative Abundance of Isotope 2)
(120.9 x 0.5721) + (122.9 x 0.4279) = 69.16689 + 52.58891
Average mass of the unknown element = 121.7558 amu
You need to monitor the solution to see when the crystals start gathering at the bottom of the solution. You can slowly add alum until it stops dissolving. The point just before it starts its sedimentation at the bottom is the point when the solution is saturated.
