Which description corresponds to the Locrian mode?

The Locrian mode is characterized by a specific arrangement of whole and half steps. In this mode, there are half steps between the first and second scale degrees, as well as between the fourth and fifth scale degrees.

In the context of a natural minor scale, which the Locrian mode is derived from, the 7th degree is lowered, resulting in a unique sound. This half step arrangement creates the distinctive and somewhat unstable quality that defines the Locrian mode. Therefore, the correct description that corresponds to the Locrian mode is the first choice, where the half steps occur between notes 1-2 and 4-5.

The other options do not accurately describe the Locrian mode's half-step pattern, as each pertains to different modes or varying arrangements of half steps that do not align with the structure of the Locrian scale. Understanding the half-step placements is essential in identifying the flavor and characteristics of the different modes within music theory.