[Phil153]

[ QUOTE ]
virtually no physics background who know the answer immediately

[/ QUOTE ]
I have a degree in physics and math, whatever that's worth.

[ QUOTE ]
but I am pretty sure if you had to point to a force which facilitates diffusion, it is the electromagnetic force.

[/ QUOTE ]
There's a bit of a difference between "facilitates" and "primarily responsible for" Is English your first language?

BTW, here is what the OP said:

[ QUOTE ]
A perfume bottle is opened. A short time later, perfume molecules can be detected across the room. The perfume molecules have diffused from a region of high concentration to one of low concentration.
What force is primarily responsible for diffusion?

[/ QUOTE ]
The reason they can be detected across the room is because they moved there, ALL ON THEIR OWN. There was no force pushing or pulling them. When they collide with other molecules there is no net force acting on them on average.

Take a real world example. If I throw some dice in craps and they bounce several times before landing, what force would be primarily responsible for them ending up at the other side of the table? The force primarily responsible is my throw, as it's the only thing that gave energy to the dice. The electromagnetic interaction between the dice and table facilitated the final result, but was not primarily responsible for them leaving my hand and ending up somewhere on the table. My throw is responsible for that. Just as the existing kinetic energy of the gas molecules is primarily responsible for smelling perfume across the room.

So I think we're on the same page. The OP just did a horrible job of wording his question and then argued the point which was clearly incorrect. Chips threw a curved ball with the second law, which has nothing to do with anything.