Final answer:
Angular resolution improves with decreased sector size in telescopes, and ALMA's interferometry technique allows it to have a much better resolution compared to the Arecibo telescope.
Step-by-step explanation:
The type of resolution that improves with decreased sector size is the angular resolution in telescopes. Angular resolution is the ability of the telescope to distinguish between two close objects in the sky. Since resolution is inversely proportional to the telescope diameter, a telescope with a smaller diameter, or sector size, can have better resolution, theoretically.
The ALMA (Atacama Large Millimeter/submillimeter Array) telescope, when operating at its longest baseline, has a significantly better resolution compared to the Arecibo telescope. ALMA can achieve higher resolution by combining signals from multiple smaller dishes spaced out over a large distance, acting like a telescope with a much larger diameter. This technique is known as interferometry. The exact resolution improvement would depend on the specific dimensions and distances involved in the ALMA configuration.