25. (10 points) The salt LiBr has a Li−Br distance of 275 pm (1 pm = 10⁻¹² m) and has the NaCl structure.(A) (3 points) Draw the unit cell of the molecule.(B) (2 points) How many atoms of Li and Br are there in a unit cell?(C) (2 points) Calculate the mass of a unit cell.(D) (3 points) What is the density of LiBr?

二、問答題：（50分）21. (13 points) Consider the NO molecule:(A) (3 points) Draw the most stable Lewis structure of this molecule. What are the oxidation states and formal charges of each element?(B) (5 points) Construct the molecular orbital diagram of NO. Use the following orbital potential energies to construct the MO diagram: N 2s: −25.56 eV, 2p: −13.18 eV. O 2s: −32.38 eV, 2p: −15.85 eV.(C) (2 points) Predict the bond order and the number of unpaired electrons of NO from your results of (A) and (B).(D) (3 points) Both NO⁺ and NO⁻ are well-known in inorganic chemistry. Based on the molecular orbital diagram results in (B), what are the bond orders of these two ions? Which one of these three would have the shortest N−O bond distance? Briefly explain.

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