What is the mass of a sample of NH3 containing 3.80 × 10^24 molecules of NH3?

Assuming you’re asking for the mass in grams the formula isn’t too hard, so if I show you this, you should be able to do them from now on. Firstly, you need to convert molecules to moles. 1 mol = 6.02*10^23. Another way of writing 3.80*10^24 is 38.0*10^23.

To convert molecules to moles...

(38.0*10^23)/(6.02*10^23) = 6.31 mol
*10^23/10^23 cancels out equaling 1*

Now to convert mol to grams you have to multiply it by the molar mass (the molar mass is the mass of a single mole of the compound element). You find it by finding the amu (mass of a single molecule), by taking the mass of one hydrogen atom, multiplying it by 3, and adding the mass one nitrogen atom and changing the unit to grams.

For example: the amu (mass of a single atom) of Oxygen is 16 amu the molar mass (mass of one mole) is 16 g. Hopefully, that makes sense.

If we apply that to the problem...

Molar mass of NH3 = (1.01*3)+14.01 = 17.04 g

6.31 mol * 17.04 g = 107.5224 g (if you’re asked to round to the significant figure, the answer is 108)

The answer for this question is d. none of these