Why does the x axis of a dose-response curve use log units?

Applying logarithm to the x axis of the dose response curve is a math trick that will linearize the middle zone of the curve and will allow you to visualize better  the  EC50 of the drug. Also the numbers on the x axis are easier to write since they are larger when you apply the logarithm to the concentrations.

you didn't give any options but heres what i can tell you: an inference is likely to change based on additional observations. the latter is something that you have seen or sensed using your sensory organs while the former is like a conclusion out from what you have observed.

if you know your abc's you should be able to get your answer or just use google