(a) 3Mg(NO3)2 + 2K3PO4 = Mg3(PO4)2 + 6KNO3
(b) 3Mg2+ + 6NO3- + 6K+ + 2PO43- = Mg3(PO4)2 + 6K+ + 6NO3-
From here, net ionic equation is as following:
3Mg2+ + 2PO43- = Mg3(PO4)2
(c) Trimagnesium phosphate
(d) Spectator ions are ions that do not participate in the reaction and are present in the solution without changing their form. Here, K+ and NO3- are spectator ions.