Im a nonmetal who is solid at room tempature has 2 letters for my symbol and mass is 79

In numbering carbon atoms in the parent chain of a hydrocarbon, why would you number from right to left, rather than left to right

Diffraction is when light is bent around obstructions. which of the these observation about clouds would indicate diffraction? a) after rain storms, you can sometimes see rainbows. b) clouds are white or gray and cannot be seen through. c) on a cloudy day, the temperature tends to be cooler than a sunny day. d) the edges of dark clouds appear lighter. this

Connect the whole numbers on the periodic table to indicate what they represent?