1) 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=0.43434) A) 3.8 days B) 16.5 days C) 33 days D) 76 days Answer: Option BExplanation:t1/2 =3.8 day ∴ λ=0.693t1/2=0.6933.8=0.182 If the initial number of atom is a = A0 then after time r the number of atoms is a/20= A , we have to find t. t=2.303λlogA0A=2.3030.182logaa/20 =2.3030.182log20=16.46 days