So mol khi':n=7.84/22.4=0.35mol
vi phan ung vua du nen
Mg-->(Mg2+) + 2e
0.1................. 0.2
Al-->(Al3+) + 3e
0.3.............. 0.9
O2 + 4e --> 2 (O2-)
x...... 4x
Cl2 + 2e --> 2(Cl-)
y....... 2y
Có hệ:x+y=0.35
4x+2y=0.2+0.9
=>x=0.2
y=0.15
=>m=0.1*24+0.3*27+0.2*32+0.15*71=27.55g
=>C