Atoms And Nuclei Question 169

Question: Atomic weight of boron is 10.81 and it has two isotopes $ _{5}B^{10} $ and $ _{5}B^{11} $ . Then ratio of $ {5}B^{10}{:{5}}B^{11} $ in nature would be [CBSE PMT 1998; JIPMER 2001, 02]

Options:

A) 19 : 81

B) 10 : 11

C) 15 : 16

D) 81 : 19

Show Answer

Answer:

Correct Answer: A

Solution:

Let the percentage of $ B^{10} $ atoms be x, then Average atomic weight $ =\frac{10x+11(100-x)}{100}=10.81 $
$ \Rightarrow x=19\ \ \ \ \therefore \frac{{N_{B^{10}}}}{{N_{B^{11}}}}=\frac{19}{81} $



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