11.Suppose you have the most abundant isotope of gold (Au). How many neutrons would it have?

Neutrons = 118

The elements in nature have several types of isotopes  

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

Atomic mass is the average atomic mass of all its isotopes  

The most abundant isotope of gold (Au) is isotope Au-197

So the atomic mass of Au = 197

and the atomic number of Au = 79

Atomic mass is the sum of protons and neutrons

Atomic Number (Z) = Atomic mass (A) - Neutrons

Neutrons = A - Z

So neutrons for Au-197 :

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.