Answer is: Prepare to measure pH change.
For example for strong acid-base titration, sodium hydoxide and hydrochloric can be used.
Balanced chemical reaction: HCl + NaOH → NaCl + H₂O.
In this reaction pH of equivalence point will be always 7.
Equivalence point is the point which there is stoichiometrically equivalent amounts of acid and base.
Chemist can draw pH curve (graph showing the change in pH of a solution, which is being titrated) for titration and determine equivalence point.
Near equivalence point indicator should change color, so we must pick indicator who change color near pH of equivalence point.
I believe that the best definition of the word common in environmental science is a typical resource. A typical resource is a resource that is not hard to find and is very common. The answer to the question will hence be A.
The answer could not be the other three choices because a shared resource is a resource that is used by more than one organism in the environment. A worthless resource is one that has no use in the environment while a rare resource is one that is hard to find.
The answer is the reaction ins a cold pack
Its a compound because they come together