Which radioactive isotope would have the longer half- life 15O or 19O? (Given rate constants for 15O and 19O are 5.63x 10-3 s -1 and k = 2.38 x 10-2s -1 respectively.)

These are the options for the question :Which radioactive isotope would have the longer half- life 15O or 19O? (Given rate constants for 15O and 19O are 5.63x 10-3 s -1 and k = 2.38 x 10-2s -1 respectively.)

a. 15O
b. 19O
c. Both will have the same half-life
d. None of the above, information given is insufficient

The correct answer is -a. 15O
The rate constant for the decay of O-15 is less than that for O-19 . Therefore ,
the rate of decay of O-15 will be slower and will have a longer half life .