Answer:
C) 132.9 amu
Explanation:
Data Given:
Abundance of Cs-133 = 75 % = 0.75
mass of Cs-133 = 133 amu
Abundance of Cs-132 = 20 % = 0.20
mass of Cs-132 = 132 amu
Abundance of Cs-134 = 5 % = 0.05
mass of Cs-134 = 134 amu
Average atomic mass of cesium = ?
Solution:
formula used to check average atomic mass is as under
Average atomic mass = m₁A₁ + m₂A₂ + m₃A₃
Where
m₁ , m₂ and m₃ = mass of isotope 1 , 2 and 3 respectively
A₁ , A₂ and A₃= abundance or fraction of isotope 1, 2 and 3 respectively
Put values in above formula
Average atomic mass = (133 amu)(0.75) + (132 amu)(0.20)+(134 amu)(0.05)
Average atomic mass = 99.75 + 26.4 + 6.7
Average atomic mass = 132.85 amu
So
Round to four significant figures
Average atomic mass of Cs = 132.9 amu
option C is correct
