Answer :

In beta decay, a neutron decays into a proton, an electron and an antineutrino.

n(neutrino) e-(electron) + e+(proton) + 𝜈+(antineutrino)


6C8(Carbon) 7N7(Nitrogen) + e-(electron) + 𝜈+(antineutrino)

The radioactive decay law is given by N = N0e-λt, where N = final number of particles, N0 = initial number of particles, λ = decay constant, t = time.

Now, , where t1/2 = half life.

In this problem, t1/2 = 12.5 yr


Hence, after a time t = 25 years,

Fraction remaining undecayed = (Ans)

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