NEET Physics Nuclei Questions Solved

The half life of radioactive Radon is 3.8 days. The time at the end of which 1/20 th of the Radon sample will remain undecayed is
(Given log10e=0.4343
(a) 3.8 days               (b) 16.5 days
(c) 33 days                (d) 76 days

(b) By the formula N=N0e-λt
Given NN0=120and λ=0.69313.820=e0.6931×t3.8 
Taking log of both sides
or log 20=0.6931×t3.8log10e
or 1.3010=0.6931×t×0.43433.8t=16.5 days

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