Question

Two isotopes of hypothetical element X exist with abundances of 30.00% 100X and 70.00% 101X. What is the approximate atomic mass of X (in atomic units, amu)?
(A) 100.3
(B) 100.5
(C) 100.7
(D) 101.0

Answer 1

Answer:

C. 100.7 amu

Explanation:

Isotopes of an element are atoms of an element with the same atomic number but different atomic masses. Each atomic mass of an isotope is known as an isotopic mass. An element that exhibits isotope, that is, that have two or more isotopes has a relative atomic mass that is not a whole number.

Relative atomic mass of X is the sum of the products of the relative abundances of each isotope and its isotopic mass.

For Isotope ¹⁰⁰X: 30% × 100 = 30 amu

For Isotope ¹⁰¹X: 70% × 101 = 70.7 amu

Relative atomic mass of X = (30 + 70.7) amu = 100.7 amu

Therefore, the approximate atomic mass of X is 100.7 amu