In the fifth group, `(NH_4)_2 CO_3` is added to precipitate out the carbonates, we do not add `Na_2 CO_3` because
A. `MgCO_(3)` is soluble in `Na_(2)CO_(3)`
B. `Na_(2)CO_(3)` increases the solubility of fifth group carbonates
C. `MgCO_(3)` will also be precipitated out in fifth group
D. `Na_(2)CO_(3)` will decrease the solubility product of `MgCO_(3)`
