Atomic Structure

Step 1: Identify given data
- Isotope 1 mass =

10%20%5C%2C%20%5Ctext%7Bu%7D

(80% abundance)
- Isotope 2 mass =

15%20%5C%2C%20%5Ctext%7Bu%7D

(20% abundance)
Step 2: Calculate average atomic mass

%5Ctext%7BAverage%20mass%7D%20%3D%20%5Cleft(%5Cfrac%7B80%7D%7B100%7D%20%5Ctimes%2010%5Cright)%20%2B%20%5Cleft(%5Cfrac%7B20%7D%7B100%7D%20%5Ctimes%2015%5Cright)

%3D%20(0.8%20%5Ctimes%2010)%20%2B%20(0.2%20%5Ctimes%2015)

%3D%208%20%2B%203%20%3D%2011%20%5C%2C%20%5Ctext%7Bu%7D

Step 3: Verify calculation
- Contribution from lighter isotope:

10%20%5Ctimes%200.8%20%3D%208%20%5C%2C%20%5Ctext%7Bu%7D

- Contribution from heavier isotope:

15%20%5Ctimes%200.2%20%3D%203%20%5C%2C%20%5Ctext%7Bu%7D

- Total average mass =

8%20%2B%203%20%3D%2011%20%5C%2C%20%5Ctext%7Bu%7D

Step 4: Match with options
The calculated average mass of

11%20%5C%2C%20%5Ctext%7Bu%7D

corresponds to option (b).

Chapter Questions
1 MCQs