Question

A hypothetical element Z exists in nature as two isotope's Z^65 and Z^67with their relative abundance 25% and 75% respectively. Then, the average atomic mass (in u) of element Z is:
(A) 65.5
(B) 66
(C) 66.25
(D) 66.5
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Answer 1

Answer:

Explanation:

For the hypothetical element, Z, the two isotopes are Z-65 and Z-67

So, average atomic mass of the element Z is (65x25)/100 +(67x75)/100

                                                                         = 65/4 + 67x3/4

                                                                         = 65/4 + 201/4

                                                                         = 266/4

                                                                         = 66.5 U

Hence the average atomic mass of the element Z is 66.5 U.

Answer 2

Answer:

Concept:

The average atomic mass of an element is the sum of the masses of its isotopes, each multiplied by its natural abundance

Explanation:

$Avg \ atomic \ mass \ of Z=\% age \ abundance \ of z 65+\% age \ abundance of z 67 \\\\So \ avg \ atomic \ mass \ of \ z=25 / 100 \times 65 +75 / 100 \times 67 \\\\ =65 / 4+201 / 4 \\ =66.25$

Hence, the option (C) is  correct answer.

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