Half-lives of two radioactive substances A and B are respectively

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Half-lives of two radioactive substances A and B are respectively 20 minutes and 40 minutes. Initially, the samples of A and B have equal number of nuclei. After 80 minutes the ratio of remaining numbers of A and B nuclei is

1. 1 : 16
2. 4 : 1
3. 1 : 4
4. 1 : 1

Correct Option: C

80 = 20 × n_A ⇒ n_A = 4
80 = 40 × n_B ⇒ n_B = 2

		=		1		²
	N_A			2
	N_B			1		²
				2

=	1	×	1	=	1
	2		2		4