Question

The average atomic mass of fictitious element Z is 261.4 amu. Z has only 2 isotopes. One of its isotopes has an atomic mass of 260.0 amu the other 264.0 amu. Choose the abundance for the isotopes

55%

44%

35%

99%

25%

1%

11%

65%

Answer 1

The abundance for the isotopes = 65%(isotope 1) and 35%(isotope 2)

Further explanation

The elements in nature have several types of isotopes

Isotopes are atoms whose no-atom has the same number of protons while still having a different number of neutrons.

So Isotopes are elements that have the same Atomic Number (Proton)

Atomic mass is the average atomic mass of all its isotopes

Mass atom X = mass isotope 1 . % + mass isotope 2.%

The average atomic mass of fictitious element Z is 261.4 amu

isotopes 1 = 260, x%

isotopes 2 = 264, 100-x%

`\tt avg~atomic~mass=260x\%+264(100-x)\%\\\\261.4=2.6x+264-2.64x\\\\0.04x=2.6\\\\x=65`