5 mg iodine 131 its half life is 8.1 days what is the time when 1% remain

Answer 1

k = 0693/t_1/2
Solve for k and substitute into the equation below.

ln(No/N) = kt
Use 5mg for No.
Use 1% x 5 = 0.05 for N.
k from above.
Solve for t.
t will be in days if you used 8.1 days for the half-life.