Predict if the following conditions would result in the formation of a preecipitate:
a. 0.0025 M Fe3+ at pH 6.00
b. 0.0025 M Ba2+ and a 1.25x10-4 M solution of sodium sulfate
c. 0.05 M Ca2+ and a 1.25 x 10-4 M solution of cesium phosphate
d. 7.92 x 1--15 M solution of Hg2+ and a saturated solution of H2S at a pH of 0.5.