Final answer:
The Hertzsprung-Russell (H-R) diagram relates the luminosity of stars to their surface temperature, with luminosity on the vertical axis and temperature on the horizontal axis, increasing leftward.
Step-by-step explanation:
The Hertzsprung-Russell (H-R) diagram relates two specific quantities for stars, which are luminosity and surface temperature. This diagram is a plot where the vertical axis represents the luminosity of a star, while the horizontal axis plots the star's temperature, increasing toward the left. On the H-R diagram, most stars are found along the main sequence, where high-mass stars with high temperature and luminosity differ from low-mass stars, which are cooler and less luminous. The position of a star on the main sequence is determined primarily by its mass, with high-mass stars being hotter and more luminous than their lower-mass counterparts.
Different regions of the H-R diagram correspond to different types of stars, such as white dwarfs, giants, and supergiants, each occupying specific areas on the diagram. As a star ages, its temperature and luminosity change, which implies that on the H-R diagram, it will 'move' to reflect these changes as it evolves.
The correct answer to the student's question is b) X: Temperature, Y: Luminosity.