According to reference table N, which pair of isotopes spontaneously decays?

(1) C-12 and N-14


(2)C-12 and N-16


(3) C-14 and N-14


(4)C-14 and N-16





i know the answer is (4) but why?

According to reference table N, which pair of isotopes spontaneously decays?
Because reference table N says so. Basically, it has a mix of protons and neutrons in the nucleus that is unstable, and that's why it decays. Other isotopes are more stable.
Reply:(3) C-14 and N-14
Reply:You did not give us nor refer us to the unknowable reference table N. So we do not know what you are talking about. The answerer who replied that the nuclei in (4) have an excess of neutrons to protons was correct. So award him full points.
Reply:Calculate the proton to neutron ratios for all of the species. These are fairly smaller species so you want an Z/N ratio right around 1. Species with ratios less than 1 are NOT stable.





(1)C-12 and N-14 are 1.00 exactly


(2) C-12 wouldn't decay but N-16 would (7 protons/9 neutrons)


(3) C-14 isn't stable but N-14 has a ratio of 1.00 so it is


(4) both are unstable so decay happens
Reply:only in 4 both isotopes are unstable and therefore radioactive. C-12 and N-14 are the stable, most abundat isotopes of carbon and nitrogen. they practically do not decay.