Predict whether a precipitation reaction will occur in each of the following situations. Write a net ionic equation for each reaction that occurs.

(a) NiCl₂(aq) + (NH₄)₂S(aq) → ?
(b) Na₂CrO₄(aq) + Pb(NO₃)₂(aq) → ?
(c) AgClO₄(aq) + CaBr₂(aq) → ?
(d) ZnCl₂(aq) + K₂CO₃(aq) → ?