Final answer:
Temperature and luminosity are the 2 characteristics used to classify stars on an H-R Diagram. The correct answer is A) Temperature and Luminosity.
Step-by-step explanation:
The 2 characteristics that are used to classify stars on an H-R Diagram are Temperature and Luminosity.
The H-R Diagram, or Hertzsprung-Russell Diagram, plots temperature along the horizontal axis and luminosity along the vertical axis.
By analyzing a star's temperature and luminosity, its position on the diagram can be determined, which provides information about its characteristics.
Therefore, the correct answer is A) Temperature and Luminosity.