Is cl- or ethanol more likely to diffuse across the plasma membrane?
a. ethanol
b. cl-?

The answer for this question would be ethanol

A non-polar molecule can diffuse plasma membrane easily but charged/polar molecule didn't. It was because the plasma membrane has negative charge. Ethanol is organic molecule that wasn't have high polarity. Ethanol size is also small, make it easy to diffuse.
Chlorine is eletrolyte that will be strictly regulated and have negative charge so tt shouldn't be able to across plasma membrane easily.