Atomic mass of nitrogen is 

Explanation:

• Atomic Mass Unit (u): The atomic mass of an element is typically expressed in atomic mass units (u).
• Nitrogen's Atomic Mass: Nitrogen has an atomic mass of approximately 14.007 u, which is often rounded to 14 u for simplicity.
• Incorrect Options:
  • 28 g and 28 u: These values correspond to the molecular mass of nitrogen gas (N₂), not the atomic mass of a single nitrogen atom.
  • 14 g: This represents the molar mass of nitrogen, indicating that one mole of nitrogen atoms weighs 14 grams, but it does not reflect the atomic mass in atomic mass units.

Therefore, the atomic mass of a single nitrogen atom is best represented by 14 u.