What is ph?
a. how basic a solution is
b. the concentration of hydrogen ions in a solution
c. the concentration of potassium ions in a solution
d. how acidic a solution is

An empty fuel tank can still contain and therefore can be even more dangerous than one full of liquid fuel.

The volume of helium in a blimp is 6.28 x 10^9 millimeters. the density of helium in the blimp is .1786 kilogram/meter^3. find the mass of the helium in the blimp.

The human eye contains a molecule called 11-cis-retinal that changes shape when struck with light of sufficient energy. the change in shape triggers a series of events that results in an electrical signal being sent to the brain that results in vision. the minimum energy required to change the conformation of 11-cis-retinal within the eye is about 164 kj/mol.