What do the symbols in the parentheses indicate

Which function is performed by earths atmosphere? a. ultraviolet rays are prevented from reaching the ozone layer. b. earths temperature is raised and moderated by trapping in heat c. charged particles from the sun are prevented from reaching earth. d. magnetic charges from space are prevented from reaching earths surface.

How many moles of gas are present if p=11 atm, v=12l, t=185k?

At stp, which substance is the best conductor of electricity? a. nitrogen b. neon c. sulfur d. silver