Answer:
PC3 12800
Explanation:
The RAM which should Jessica purchase so that she can use a quad channel on her motherboard is the PC3 12800 because it supports 1600 MHz modules while the other RAMs such as PC4 24000, PC3 1600 and PC3 10600 does not support 1600 MHz modules so that's why Jessica shouldn't purchase any of these RAMs and prefer PC3 12800 over the others.
PC3 12800 is recommended as she has a motherboard can hold 16GB of RAM and has four slots. Moreover She also has two DDR3 DIMM modules that are labeled 1600 MHz.