Final answer:
The reaction between lead nitrate and potassium sulfate forms an insoluble solid, lead sulfate, characterizing it as a precipitation reaction.
Step-by-step explanation:
The reaction Pb(NO₃)₂(aq) + K₂SO₄(aq) → PbSO₄(s) + 2 KNO₃(aq) is best classified as a precipitation reaction. This reaction involves the formation of an insoluble solid, known as a precipitate, from the combination of two aqueous solutions. In this case, lead sulfate (PbSO₄) is the precipitate which forms, indicating that a precipitation reaction has occurred. When more testing is directed to areas of the system that initially found more defects than average, the testing principle being applied is that defects cluster together. This principle acknowledges that defects in software are often not randomly distributed, but tend to be found in clusters.