Answer :
The average atomic mass of a fictitious element is 154.8 amu.
What is average atomic mass ?
The weighted average mass of the atoms in a naturally occurring sample of an element is the average atomic mass, also known as atomic weight. Unified atomic mass units (u), where 1 u is equal to precisely one-twelfth the mass of a neutral atom of carbon-12, are the standard units used to express average masses.
The average atomic mass of any element is given by
= [tex]\frac{atomic mass of X * percent of isotope X +mass of Y * percent of isotope Y}{percent of isotope X + percent of isotope Y}[/tex]
=[atomic mass of X * percent of isotope X +mass of Y * percent of isotope Y]/[percent of isotope X + percent of isotope Y]
where
atomic mass of X=155.8 amu
atomic mass of Y=153.7 amu
percent abundance of isotope X = 52.45%.
percent abundance of isotope Y = 47.55%.
average atomic mass of fictitious element is
=[155.8 * 52.45 + 153.7 * 47.55]/{52.45 + 47.55]
= 154.80145 ≅ 154.80 amu
So the average atomic mass of a fictitious element is 154.80 atomic mass unit.
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