The molar mass of NH3 is 17.03 g/mol. To calculate the number of moles in 4.00 g of NH3, we can use the following formula:

Moles = Mass (in grams) / Molar Mass (in g/mol)

Substituting the given values, we get:

Moles = 4.00 g / 17.03 g/mol

Therefore, there are approximately 0.235 moles of NH3 in 4.00 g of NH3.