Radioactivity — Question 10

Which of the following is the radio isotope in each pair (a), (b) and (c) ?

(a) $_{6}^{12}\text{C}$, $_{6}^{14}\text{C}$

(b) $_{15}^{30}\text{P}$, $_{15}^{32}\text{P}$

(c) $_{19}^{39}\text{K}$, $_{19}^{40}\text{K}$

Give reason for your answer.