Ahertzsprung-russell diagram is used to show the relationship between
a. absolute magnitude and apparent magnitude.
b. temperature and absolute magnitude.
c. parallax and temperature.
d. apparent magnitude and parallax.

(B) Temperature and absolute magnitude.

Explanation:

 The relationship between the temperature and the absolute magnitude are shown by the H-R diagram (Hertzsprung-Russell diagram). The Hertzsprung-Russell diagram is also known as color- magnitude diagram.

 In the Hertzsprung–Russell outline, it is a disperse plot of stars indicating the connection between the absolute temperature versus their outstanding arrangements or viable temperatures. It is mainly used in the form of graphical tool which is used to classifying the stars according to the magnitude and also temperature.

Therefore, Option (B) is correct.