Hey there!
A mole is measured in atoms, molecules, particles. It's kind of a loose sort of measurement, just unit of the substance.
Since there is a ratio of 1 to 1 nitrogen to oxygen, there will be the same amount of molecules as atoms of nitrogen.
2.25 moles of NO gas are formed from 2.25 moles of nitrogen.
Hope this helps!
First, determine the number of moles of gold.
Number of moles = 
Given mass of gold =
Molar mass of gold = 196.97 g/mol
Put the values,
Number of moles of gold = 
=
or
Now, molarity = 
Put the values, volume of ocean =
Molarity = 
= 
Thus, average molar concentration = 