(b) t½ = (ln 2) / λ = 0.693 / λ so λ = 0.693 ÷ 23.5 = 0.0295 min-1 N = Noe−λt so N / No = e−(0.0295 x 141) = 0.0156 Percentage remaining = (N / No) x 100 = 1.56%.This can more easily be solved by inspection. 141 minutes is equal to 6 half-lives. 1 → 0.5 → 0.25 → 0.125 → 0.0625 → 0.03125 → 0.0156 (i.e. 1.56 %)(c) Three neutrons produced since:2. Each element has its own specific absorption spectrum...