Final answer:
A balanced chemical equation is required to calculate the moles of NH3 from the moles of N2H4. The question provides an incomplete reaction, which makes it impossible to perform the stoichiometric calculation as presented.
Step-by-step explanation:
This question involves stoichiometry, which is a concept in Chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. To calculate the moles of NH3 formed when 4.2 moles of N2H4 completely reacts, we first need the balanced chemical equation. However, the equation provided in the question, N2H4 (l) → NH3(g) + N2(g), is incomplete and does not reflect the actual reaction.
Assuming the balanced equation is: N2H4 + 2H2 → 2NH3 + N2, we could use the stoichiometric ratios to find the answer. Unfortunately, with the provided equation and information, it's not possible to calculate the moles of NH3 based on the moles of N2H4. We need a balanced equation relevant to N2H4 for an accurate calculation.