Your understanding of the subject appears correct, but be careful with the wording. The quesion asks "which of the following statements would be
incorrect?" So which one is wrong?
With thrust reverse fully deployed, the cold stream air (low bypass) thrust would increase, and the hot air (core) would still increase as that's where the thrust is produced.
So B) Forward thrust from the hot gases would decrease....is wrong, which is why it's right
