Multiple choice Given t1/2 of A is 1000 years. What will be value of A after 2000 years? 50% 25% 12.5% 6.725% Reveal answer Fill a bubble to check yourself B Correct answer Explanation It has been calculated as under: No. of half lives = 2000/1000 = 2. Amount of substance left after n half lives =N0/2n = 1/4 = 0.25 or 25%.