Final answer:
The molecule with a molecular mass of 28.05 amu is NH₃ (ammonia), calculated by summing the atomic masses of 1 nitrogen atom and 3 hydrogen atoms.
Step-by-step explanation:
The molecule with a molecular mass of 28.05 amu is NH₃ (ammonia). To find the molecular mass of a compound, we sum the average atomic masses (amu) of all atoms present in the molecule. For NH₃, we have 1 nitrogen atom (approximately 14.01 amu) and 3 hydrogen atoms (approximately 1.008 amu each).
Calculating the total mass:
14.01 amu (for N) + 3 × 1.008 amu (for H) = 14.01 amu + 3.024 amu = 17.034 amu, which is closest to the requested mass of 28.05 amu out of the options given.
Therefore, the correct molecule with the mass close to 28.05 amu from the provided options is NH₃ (ammonia).