Which statement about luminosity is not true? a. it is commonly measured in watts. b. it is valued at 1 for our sun. c. it stands for the total energy output of a star d. it increases from top to bottom on an h-r diagrams

D. It increases from top to bottom on an H-R diagrams 

Luminosity is defined in the wordbook as brightness of a celestial object. In astronomy, it stands for the total amount of energy emitted per unit time by a star, so C. is correct. It is measured in joules per second or watts so A is correct also. It is B,  valued at 1 for our sun.

In an H-R  diagram, the energy of a star is plotted on the vertical axis. The lower or more negative the measure, the brighter the star, D is therefore not true.