SE APLICA RELATIA : n,mol= m,g/M,g/mol
M= (3x1gH+ 31gP+4x16gO)/mol=98g/mol
n= 490g/98g/mol=..............................calculeaza !
daca nu stii formula ,aplici reagula de trei simpla
98g...este masa .......1mol
490g............................x= 490/98mol=.....................