Answer:
screen resolution
Step-by-step explanation:
The screen resolution indicates the number of pixels that can be displayed at one time on a given screen. For example, it could be numbers like 1920x1080, 1600x900 and so on.
Viewing angle has nothing with the pixel count, although viewing port would. Color depth concerns the number of colors you can display at one time. Pixel density is the concentration of pixels, like in Apple's retina display, that increases the number of pixels in the screen, but that doesn't give you the information on how many there are.