Question

The atomic symbol mc025-1.jpg represents potassium-40 (K-40), a radioactive isotope that has 19 protons and 21 neutrons. Which atomic symbol could represent an isotope that results from the decay of K-40?
a) 40 Ar
18

b) 40 K
18

c) 42 Ca
20

d) 42 K
20

Answer 1

The answer is a 40/18Ar

Answer 2

Answer: The correct option is A.

Explanation: For a radioactive isotope of potassium, which is $^{40}K$ having 19 protons and 21 neutrons, the decay processes are beta-decay and electron capture.

Potassium-40 undergoing decay processes:

• Electron Capture: In this process, the unstable nuclei becomes stable by converting electron into neutron with the help of proton.

$_{19}^{40}\textrm{K}\overset{\text{electron capture}}{\rightarrow} _{18}^{40}\textrm{Ar}$

• Beta-decay: In this process, the unstable nuclei becomes stable by converting a neutron into proton and electron.

$_{19}^{40}\textrm{K}\overset{\beta \text{-decay}}{\rightarrow} _{20}^{40}\textrm{Ca}$

From the two processes, the K-40 isotope forms $_{18}^{40}\textrm{Ar}$ by electron capture. So, the correct option is A.