Answer:
the correct answer is option c
Step-by-step explanation:
the half-life of material 2 is 30 hours more than the half-life of material 1
that is, ∆the half-life of the material 2 > ∆the half-life of material 1 by 30 hours (I.e the time taken to deplete up to its half from 60 hours to 30 hours)