Question

which two characteristics are used to classify stars on the hertzsprung-russell diagram?
○ size and density
○ density and composition
○ composition and temperature
○ temperature and absolute brightness

Explanation:

The Hertzsprung-Russell (H-R) diagram is a key tool in astronomy that plots stars based on two core properties: their surface temperature (or spectral class, which correlates with temperature) on the horizontal axis, and their absolute brightness (luminosity) on the vertical axis. The other listed pairs of characteristics are not the primary classification metrics for this diagram.

Answer:

temperature and absolute brightness