bài 1:
nO2= 3*10^24/6*10^23=5 mol
=> VO2= 5*22.4=112 lít
bài 2:
đổi 1kg = 1000g
mC= 1000*96%=960 g
=> nC= 960/12=80 mol
pthh: C + O2----t0-----> CO2
.......80.....80......................mol
=> VO2= 80*22.4=1792 lít
bài 3:
a) nP=6.2/31=0.2 mol
nO2= 6.72/22.4=0.3 mol
pthh :    4P + 5O2----t0----> 2P2O5
theo pt : 4........5..................2
theo đb: 0.2....0.3...................mol / P pư hết , O2 dư
theo pư:0.2.....0.25.............0.1mol
sau pư: 0........0.05.............0.1mol
mO2 dư = 0.05*32=1.6 g
b) mP2O5= 0.1*142=14.2g