The experimental apparatus represented above is used to demonstrate the rates at which gases diffuse. When the cotton balls are placed in the ends of a tube at the same time, the gases diffuse from each end and meet somewhere in between, where they react to form a white solid. Which of the following combinations will produce a solid closest to the center of the tube?
a. HCI and CH3NH2
b. HCl and NH3
c. HBr and CH3NH2
d. HBr and NH3