Answer:
5) 24.3 amu
6) 193 amu
7) 6.94 amu
Step-by-step explanation:
The fractional abundance shows how many atoms of the element exist as a particular isotope with a certain mass.
To find the average, multiply the fractional abundance with the mass. All the fractional abundance should add up to 100%.
5) Average atomic mass of Mg
= 78.7%× 23.985 +10.13% ×24.986 +11.17% ×25.983
= 24.3 amu (3 s.f.)
6) Avg atomic mass
= 37.85% ×191 +62.42% ×193
= 193 amu (3 s.f.)
7) Avg atomic mass
= 7.59% ×6.015 +92.41% ×7.016
= 6.94 amu (3 s.f.)
*amu stands for atomic mass units