Complete the missing components/variables given as x and y in the following reactions:
(i) Pb(NO3)2(aq) + 2KI(aq) -----> PbI2(x) + 2KNO3(y)
(ii) Cu(s) + 2AgNO3(aq) ------> Cu(NO3)2(aq) + x(s)
(iii) 2n(s) + H2SO4(aq) ------> ZnSO4(x) + H2(y)
(iv) CaCO3(s) +x -----> CaO(s) + CO2(g)