How many molecules in 3 moles of ammonia nh3?

By definition, each mole contains Avogadro's Number of molecules. Therefore, 3 moles contain about 3 X 6.022 X 1023 or about 1.807 X 1024. If the number of moles is not considered to be an exact integer, this should be written as 2 X 1024 in order to avoid unjustifiably many significant digits.