A bar graph uses bars of different widths although all represent the same category level. Why is this inappropriate?

Correct answer: Width may also create a false impression of quantity

The governing principle is faithful visual encoding. In a standard bar graph, equal categories should use equal-width bars, while the bar length or height represents the value. If width also varies without a stated meaning, viewers may judge area as well as length and believe a value is larger than it is. Thus option B is correct; the other effects do not follow from unequal bar widths.