Please help! Super confused myself :(

Hello, can someone please help me with the last two parts. I understand part (a) I am just super confused by what to do and looking at the mark scheme did not help!

This is a question from AQA Chemistry Unit 1 January 2013 paper!

Thank you!

Ammonia is used to make nitric acid (HNO3) by the Ostwald Process.
Three reactions occur in this process.

Reaction 1 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)
Reaction 2 2NO(g) + O2(g) → 2NO2(g)
Reaction 3 3NO2(g) + H2O(I) → 2HNO3(aq) + NO(g)

5 (a) In one production run, the gases formed in Reaction 1 occupied a total volume of 4.31m3 at 25ºC and 100kPa. Calculate the amount, in moles, of NO produced. Give your answer to 3 significant figures. (The gas constant R = 8.31J K–1mol–1)

............................................................................................................................................
5 (b) In another production run, 3.00kg of ammonia gas were used in Reaction 1 and all of the NO gas produced was used to make NO2 gas in Reaction 2. 5 (b) (i) Calculate the amount, in moles, of ammonia in 3.00kg.

............................................................................................................................................
5 (b) (ii) Calculate the mass of NO2 formed from 3.00kg of ammonia in Reaction 2 assuming an 80.0% yield.
Give your answer in kilograms.
(If you have been unable to calculate an answer for part (b)(i), you may assume a value of 163 mol. This is not the correct answer.)

PV = nRT



divide the mass in grams by the relative mass of ammonia



Using equation 1 you can see that mol ammonia = mol NO

From equation 2 you can see that mol NO = mol NO₂

Hence mol ammonia = mol NO₂

But you only get 80%, so you must multiply your final answer by 80/100 or 0.8