Respuesta :

Atomic mass:

Mg = 24.3050 u.m.a
C = 12.0107 u.m.a
O = 15.9994 u.m.a

MgCO3 => 24.3050 + 12.0107 + 15.9994 x 3 => 84.3139 g/mol

hope this helps!