Question

A newly discovered element, Z, has two naturally occurring isotopes. 90.3 percent of the sample is an isotope with a mass of 267.8 u, and 9.7 percent of the sample is an isotope with a mass of 270.9 u. What is the weighted average atomic mass for this element? (2 points)

A)268.1 u

B)269.0 u

C)269.4 u

D)270.6 u

Answer 1

the ans is (a)268..1
the fomate of finding the average is

(90.3×267.8+9.7×270.9)/100

Answer 2

Answer: The correct answer is Option A.

Step-by-step explanation:

Average atomic mass of an element is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.

Formula used to calculate average atomic mass follows:

`\text{Average atomic mass }=\sum_(i=1)^n\text{(Atomic mass of an isotopes)}_i* \text{(Fractional abundance})_i`

We are given:

Mass of isotope 1 = 267.8 u

Percentage abundance of isotope 1 = 90.3 %

Fractional abundance of isotope 1 = 0.903

Mass of isotope 2 = 270.9 u

Percentage abundance of isotope 2 = 9.7%

Fractional abundance of isotope 2 = 0.097

Putting values in above equation, we get:

`\text{Average atomic mass of Z}=[(267.8* 0.903)+(270.9* 0.097)]`

`\text{Average atomic mass of Z}=268.1u`

Thus, the correct answer is Option A.