Solveeit Logo

Question

Question: Half-lives of two radioactive substances A and B are respectively 20 min. and 40 min. Initially, the...

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

A

1 : 16

B

4 : 1

C

1 : 4

D

1 : 1

Answer

1 : 4

Explanation

Solution

Use, N = N0/2n Ž NA = N0280/20=N024\frac { N _ { 0 } } { 2 ^ { 80 / 20 } } = \frac { N _ { 0 } } { 2 ^ { 4 } }

NB= N0280/40=N022\frac { N _ { 0 } } { 2 ^ { 80 / 40 } } = \frac { N _ { 0 } } { 2 ^ { 2 } } Ž NANB=14\frac { \mathrm { N } _ { \mathrm { A } } } { \mathrm { N } _ { \mathrm { B } } } = \frac { 1 } { 4 }

Ž NA : NB :: 1:4