How did you know what to drop out in the net reaction?First reaction
NiSO4 + Na2CO3 ==> NiCO3 + Na2SO4
Ni++(aq) + CO3--(aq) ==> NiCO3(s)
NiCO3 + HCl ==> NiCl2 + H2CO3
In aqueous solution, H2CO3 decomposes to CO2 and H2O. This is just a fact you should know. It's the same vinegar/baking soda experiment principle everyone has seen.