1) Half-life of an element is t second. Calculate the percentage left undecayed in t/2 sec. 2) 54.5 mg Na3PO4 contains 32^P (15.6%) and 31^p atoms. Assuming only 32^p atoms are radioactive, calculate the rate of decay for the given sample of Na3 PO4. The half-life period of 32^P = 14.3 days; mol. wt. of Na3PO4 = 161.2.