Answer: A short incubation time runs the risk of a false negative on the VP test, since not enough time may have elapsed to produce an adequate amount of acetoin to give a positive result. The pH change associated with mixed acid fermentation occurs fairly quickly and is less likely to be affected by shorter incubation.
b) The VP test would benefit most from a longer incubation time because it takes a while for the 2,3-butanodiol to be produced.
Three parts of nitrogen plus five parts of phosphorous gives you a total of 8 parts (3+5=8). Nitrogen makes up only three of those eight parts, or 3/8. The correct answer is B) 3/8.
