To find the formula mass of nitrogen hydride, we need to add up the atomic masses of its constituent atoms. Nitrogen (N) has an atomic mass of approximately 14.01 atomic mass units (amu), and hydrogen (H) has an atomic mass of approximately 1.01 amu.

The formula for nitrogen hydride is NH3, which means there is one nitrogen atom and three hydrogen atoms in one molecule of nitrogen hydride. So, to find the formula mass, we multiply the atomic mass of nitrogen by the number of nitrogen atoms and add it to the atomic mass of hydrogen multiplied by the number of hydrogen atoms:

Formula mass = (Atomic mass of N x Number of N atoms) + (Atomic mass of H x Number of H atoms)

= (14.01 amu x 1) + (1.01 amu x 3)

= 14.01 amu + 3.03 amu

= 17.04 amu

Therefore, the formula mass of nitrogen hydride (NH3) is approximately 17.04 atomic mass units.