Question

noticeable tread wear on the outside edges of a tire tread pattern is a sign of
underinflation.
proper inflation.
overinflation.
tread bars.

Explanation:

When a tire is underinflated, the tire's sidewalls flex more, and the tire contacts the road over a wider area. This causes more wear on the outer edges of the tire tread. Proper inflation leads to even wear. Overinflation causes wear in the center of the tire. Tread bars are indicators of worn - out tires (when tread depth is too low), not related to edge - wear pattern.

Answer:

underinflation.