The half-life of Th is 1.9 years. If after 5.7 years the mass of Th was found to be 1.25 g. Determine the initial mass of the radioactive isotope

Question

The half-life of  is 1.9 years. If after 5.7 years the mass of  was found to be 1.25 g. Determine the initial mass of the radioactive isotope

Answer 1

No. of half life = ^5.7/_1.9  = 3

             1st                    2nd                   3rd
1.25  2.5  5.0  10.0
           =10.0g