I literally looked everywhere for the answer, and I still found nothing. I hope you get it right. Sorry.
This method is known as linear perspective.
When using linear perspective, artists use a set of drawn or imaginary lines which are made to converge at the horizon of the image. These lines change the viewer's perspective by providing a point through which the relative size, shape and position of objects is determined. This technique creates the illusion of depth.
A. krypton (atomic mass 83.8 amu)
B. argon (atomic mass 39.95 amu)
C. xenon (atomic mass 131.3 amu)
D. radon (atomic mass 222 amu)
hope this helps!
