Which of the following nuclei is most likely to decay by positron emission? explain your choice.
(a) chromium-53
(b) manganese-51
(c) iron-59

(b) manganese-51

Explanation:

Positron emission or β+ decay is emission of positron from nucleus. It is observed for the nuclides in which ratio to the neutron and the proton is low. These type of nuclides lie below band of the stability. Positron decay is conversion of proton into neutron with emission of positron.

Manganese-51 is most likely to decay by the positron emission.

The n:p ratio:

For Cr-53 is:

For Mn-51 is:

For Fe-59 is:

As stated above, positron decay occurs when n:p ratio is low.

Thus, Mn-51 has the lowest n:p ratio and therefore is likely to decay by the positron emission.