Halflife is the time taken by a radioactive substance by half its original mass. In this case the half life of the substance is 3 hours. Therefore; New mass = Original mass × (1/2)^n where n is the number of half lives. In this case, the half life is 3 hours and therefore; the number of half lives in 6 hours will be two. = if the original mass is 100% new mass = 100 × (1/2)^2 = 100 × 1/4 = 25% The remaining mass will be 1/4 of the original mass, meaning a fraction of 3/4 of the initial mass will have decayed. Thus; the answer is 3/4
