B) Calculate the relative atomic mass for magnesium using the information below (to 3 significant figures).
Magnesium has three common isotopes, magnesium-24, magnesium-25 and magnesium-26.
Their abundances are 79.0%, 10.0% and 11.0%, respectively.

Relative atomic mass  = 24.32 amu.

Explanation:

Given data:

Relative atomic mass of Mg = ?

Abundance of Mg-24 = 79.0%

Abundance of Mg-25 = 10.0%

Abundance of Mg-26 = 11.0%

Solution:

Relative atomic mass = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass) +  (abundance of 3rd isotope × its atomic mass)  / 100

Relative atomic mass  = (79.0×24)+(10.0×25) +(11.0×26) /100

Relative atomic mass =  1896 + 250 + 286 / 100

Relative atomic mass  = 2432 / 100

Relative atomic mass  = 24.32 amu.

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.