Correct Answer is: (C) 1 : 4
Key Idea :Total no. of nuclei remained after n
half-lives is N = N0 (1/2)n.
Total time given = 80 min Number of half-lives of A, nA = 80 min/ 20 min = 4
Number of half-lives of B, nB = 80 min/ 40 min = 2
Number of nuclei remained undecayed N = N0 (1/2)n where N0 is initial number of nuclei
NOTE : The graph between number of nuclei decayed with time is shown along side,