Iodine-131, t1/2 = 8.0 days, is used in diagnosis and treatment of thyroid gland diseases. if a laboratory sample of iodine-131 initially emits 9.95 × 1018 β particles per day, how long will it take for the activity to drop to 6.22 × 1017 β particles per day?

Explanation:

Formula for the first order decay is as follows.

          = -kt

where,    A = activity at time t

          = initial activity

                k = decay constant

Hence, putting the given values into the above formula as follows.

                 k =

                    =

                    = 0.086643 per day

Also,    

                        t = 32 days

Thus, we can conclude that it will take 32 days for the activity to drop to particles per day.

the answer to your question is c.

if you read the house of usher you should know that the house was haunted