Question
a radioactive substance (M= 100g/mol) have t½ of 5 days. if today 0.125mg is left over what was its activity 20 days earlier?
(a) 522.8 Ci
(b) 1.93*10^7 Rd
(c) 1.93*10^13 Bq
(d) all of these
Joshi sir comment
20 day means 4 half lifes so today 0.125mg means 0.125*24 = 2gm earlier
so activity dn/dt = kn
solve and convert in required units