Complete the missing components/variables given as $x$ and $y$ in the following reactions:
$(a)$ $Pb(NO_3)_2(aq) + 2KI(aq) \longrightarrow PbI_2(x) + 2KNO_3(y)$
$(b)$ $Cu(s) + 2AgNO_3(aq) \longrightarrow Cu(NO_3)_2(aq) + x(s)$

(A) In chemical equations,the physical states of substances are represented as $(s)$ for solid,$(l)$ for liquid,$(g)$ for gas,and $(aq)$ for aqueous solution.
$(a)$ In the reaction $Pb(NO_3)_2(aq) + 2KI(aq) \longrightarrow PbI_2(s) + 2KNO_3(aq)$,$PbI_2$ is a precipitate formed,so $x = (s)$. $KNO_3$ remains dissolved in the solution,so $y = (aq)$.
$(b)$ In the reaction $Cu(s) + 2AgNO_3(aq) \longrightarrow Cu(NO_3)_2(aq) + 2Ag(s)$,silver is displaced as a solid metal,so $x = 2Ag$.