Final answer:
A star in the lower left of the H-R diagram is smaller and cooler compared to a star in the middle.
Step-by-step explanation:
On the Hertzsprung-Russell diagram, a star in the lower left is smaller and cooler compared to a star in the middle. The H-R diagram is a plot of stellar luminosity against surface temperature, and most stars lie on the main sequence, which extends diagonally across the diagram. Stars in the lower left have lower temperature and lower luminosity, indicating that they are smaller and cooler.