Two different radioactive elements with half lives T₁ and T₂ have undecayed atoms N₁ and N₂ respectively, present at a given instant. The ratio of their activities at this instant is (a) (N₁T₁)/(N₂T₂) (b) (N₁T₂)/(N₂T₁) (c) (N₁T₂)/(T₁T₂) (d) (T₁T₂)/(N₁N₂)

Answer: (b). Activity A = λ N = (0.693)/(T)N. (A₁)/(A₂) = (N₁/T₁)/(N₂/T₂) = (N₁T₂)/(N₂T₁). So the answer is (b) (N₁T₂)/(N₂T₁).

Two different radioactive elements with half lives T₁ and T₂ have… | MHT CET 2026 (15 Apr, Shift 1)

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Law of Radioactive Decay

Two different radioactive elements with half lives $T_1$ and $T_2$ have undecayed atoms $N_1$ and $N_2$ respectively, present at a given instant. The ratio of their activities at this instant is

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Answer: (b)

Activity $A = \lambda N = \frac{0.693}{T}N$ .
$\frac{A_1}{A_2} = \frac{N_1/T_1}{N_2/T_2} = \frac{N_1T_2}{N_2T_1}$ .
So the answer is (b) $\frac{N_1T_2}{N_2T_1}$ .

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