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Question

Atomic mass of boron is 10.81. It has two isotopes namely 115B and x5B with their relative abundance of 80% and 20% respectively. The value of x is:

A
10.05
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B
10
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C
10.01
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D
10.02
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Solution

The correct option is B 10
We have,
Average atomic mass =(mass× percentage abundance of 1)+(mass× percentage abundance of 2)100

10.81 =(11×80)+(x×20)100

x=10.0510 (since mass number is a whole number)

Hence, the correct option is (B).

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