What is the percent-by-mass concentration of NaCl in a solution that is prepared by adding 30.0 g of NaCl to 90.0 g of water

Fugu, also known as puffer fish, is a sushi delicacy that can also be lethal. puffer fish contain a powerful toxin that can kill an adult a few hours after ingestion. sushi chefs who prepare fugu must be specially trained because any contamination of the toxin-free areas of the fish can be deadly. recently this toxin has been put to good use, as scientists have discovered that a purified form of it can treat severe pain in cancer patients. this recent scientific discovery would fall under which area of chemistry? applied biochemistry pure organic chemistry pure physical chemistry applied inorganic chemistry

Layers of rock containing fossils, like the layers illustrated here, are most likely composed of rocks.

Which is an example of a reversible physical change?