What does the "proof" mean on a bottle of liquor? i know that 100 proof liquor is 50% alocohol and 80 proof is 40% and so on. but where does the term "proof" come from and why display it on the bottle? why not just say 50% alcohol etc etc?

Ascientist wants to know how individual lions within a pride interact with each other in their own environment. to do this, the scientist sedates and tags all of the lions within a pride. then, he places several remotely-controlled video cameras near the lions' den and performs an observational field study. he collects continuous video footage over the span of one year, analyzes the video, and then forms conclusions based on his observations.

Calculate the ph of a .10m nh4cl solution. the kb value for nh3 is 1.8×10^-5

Silver reacts with oxygen to produce silver oxide. (write balanced chemical equation and identify type of chemical reaction.)