The mass spectrum of an element with two naturally occurring isotopes is shown below.Its average atomic mass would be best estimated as
A)less than 26 amu but greater than 25 amu.
B)less than 25 amu but greater than 24 amu.
C)equal to 24 amu.
D)equal to 25 amu.
E)greater than 26 amu.

Question

The mass spectrum of an element with two naturally occurring isotopes is shown below.Its average atomic mass would be best estimated as 
A)less than 26 amu but greater than 25 amu. 
B)less than 25 amu but greater than 24 amu. 
C)equal to 24 amu. 
D)equal to 25 amu. 
E)greater than 26 amu.

Quizplus · Accepted Answer

The peak at m/z = 10 represents the isotope with 10 neutrons, which has a relative abundance of approximately 30%. The peak at m/z = 11 represents the isotope with 11 neutrons, which has a relative abundance of approximately 70%. To calculate the average atomic mass, we multiply the mass of each isotope by its relative abundance, sum the products, and divide by 100. (10 amu × 0.30) + (11 amu × 0.70) = 10.7 amu. Therefore, the average atomic mass would be best estimated as less than 25 amu but greater than 24 amu. The correct answer is B.

The Mass Spectrum of an Element with Two Naturally Occurring