A student adds 10.0 mL of 0.10 M aqueous sodium sulfate to separate 10.0 mL samples of 0.10 M aqueous solutions of four different metal(II) nitrates at 25 °C. According to standard solubility rules, which metal(II) nitrate will produce a visible precipitate immediately upon mixing?
a) magnesium nitrate
b) copper(II) nitrate
c) lead(II) nitrate
d) potassium nitrate