Explanation:
To find the molar mass of NH3 you need to look at the periodic table for the atomic mass of N (nitrogen) and H (hydrogen).
There, you can find the following atomic masses:
N - 14 g/mol
H - 1 g/mol
Then, you just calculate the molar mass by multiplying the atomic mass of the element by the quantity of atoms of it. We have 1 atom of nitrogen and 3 atoms of hydrogen, so:
(14*1)+(1*3) = 17 g/mol
Answer: 17 g/mol
