Two substance a and b are present such that [a]=4[b] and half life of a is 5 min and of b is 15 min ...

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inital conc. Ao=4Bo A conc. decs. as 4Bo=>2Bo=>Bo=>0.5Bo B conc. decs. as Bo=>0.5Bo thus, one half life of Bo=three half life of Ao                                       =15 mi...