1cmcub are masa.....3,9gAl2O3
0,250cmcub...............m=0,975g
M,Al2O3= (2X27gAl +3x16gO)/mol= 102g/mol
n=m/M; n=0,975g/102g/mol= 0,0095molAl2O3
1molAl2O3.........2mol atomiAl
0,0095mol...........n= 0,019mol atomiAl
1mol atomiAl.............6,023x10²³atomi
0,019mol......................N= 0,019x6,023x10²³atomi...............calculeaza !!!!