What is litmus paper? How is it used to determine if a compound is an acid or base?

Litmus paper is a tool used to test whether a substance is an acid or base. When a substance is dissolved in water, the resulting solution causes the litmus paper to change color. The acidity or alkalinity of a solution is determined by the concentration of hydrogen ions, or power of hydrogen, expressed as a pH value.

(I think this is right I'm not totally sure.)

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.

idk why hjggjhjkhj