2K⁺(aq) + S²⁻(aq) + Pb²⁺(aq) + 2NO₃⁻(aq) → PbS(s) + 2K⁺(aq) + 2NO₃⁻(aq)
As you can see on both side of the equation we have K⁺ and NO₃⁻ ions. They do not participate in the reaction, and they are called spectator ions. All the above is an ionic equation.
When we cancel out spectator ions, it remains just ions and molecules involved in the reaction and we get the net ionic equation:
S²⁻(aq) + Pb²⁺(aq) → PbS(s)
