What color is associated with a cloudless sky?

The term that is associated with a cloudless sky is "azure." This word specifically refers to the bright blue color often seen on clear days, reflecting the typical appearance of a cloud-free sky. Azure conveys a vivid, deep blue shade that is commonly associated with ideal weather conditions and summery skies, making it an apt descriptor when envisioning a perfectly clear atmosphere.

In contrast, the other options do not relate to the color of a sky. "Capacious" refers to space or capacity, "copious" signifies something abundant or plentiful, and "acrid" describes a sharp or bitter taste or smell. Thus, none of these words connects to the imagery of a clear blue sky, reinforcing that azure is the correct choice.