A student mixes 5.00 mL of 2.00 x 10-3 M Fe(NO3)3 with 5.00 mL 2.00 x 10-3 M KSCN. She finds that in the equilibrium mixture the concentration of FeSCN+2 is 1.40 x 10-4 M.

Radon-222 or rn-222 has a half-life of 3.82 days. to determine the fraction of an original sample of rn-222 that remains unchanged after 7.646 days, we calculate the amount of rn-222 remaining after 7.646 days and divide it with the original amount. using 1 gram as a basis and using half-life calculation methods, we can determine that  0.249 or 0.25  grams of rn-222 will remain, and thus the fraction remaining is 0.25 or 1/4.