Why are there display chemical safety symbols at the entrances of buildings?

Why should xylem tissue be dead? A thick clear mucus that cleanses the urethra of acidic urine? What is the range of beta radiation? What is the importance of reflex testing in a physical exam? Does any US state have perfectly square or rectangular borders? How many chromosomes are present in an egg just produced by the ovaries? Through which four South American countries does the 20 degree south line of latitude pass? Is a cress plant a annual or perennial? What do geologists call a volcano if it never erupts again? How many earthquakes erupt each year? Can you give your dog your probiotic? Why cholroform is rarely used as solvent in recording uv spectrum? What is 237 cm in feet? What is 23 degrees north latitude and 23 degrees south latitude? What city is located at 14 north and 120 east? Which states in Australia would include the coordinates 43 degrees S latitude 148 degrees E longitude? What are four ways a fossil can be destroyed once it become a fossil explain what happens for each? What is the altitude in El Calafate? What is the sequential process of waste removal from the human body? Why are the properties of different compounds so different from each other?