Free Response - Solve each problem, showing all work. Partial credit may be given.

1. An unknown element X has 4 naturally occurring isotopes. The isotopic masses (u) and
percent abundance of the isotopes are given in the table below.

Mass (u)
Natural
Isotope
Abundance
X₁
X2₂
X3
X4
49.9460
51.9405
52.9407
53.9389
a. Determine average atomic mass of this element.
b. Identify the element.
4.345%
83.789%
9.501%
2.365%
c. State the number of protons and neutrons in each isotope.
An isotope (X5) of this element has been synthesized in the lab. This isotope has a half-life of
27.7 days.
d. How long will it take for 600 g of the substance to decay to 75 g?