A radioactive nucleus decays by two different processes. The half life for the first process is 10 s and that for the second is 100 s. The effective half life of the nucleus is close to :

If a radioactive sample undergoes two processes simultaneously then  dNdt=−λ1N−λ2N=−λ1+λ2N=−λeffNGiven half life of the processes  10=ln2λ1,100=ln2λ2Effective process half life =  ln2λeff=ln2λ1+λ2=1110+1100=10011≈9s