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 :

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements