Sometimes when performing a crystallization, one solvent alone will not work and you have to use a solvent-pair. will the solvent pair pentaine and water work? why or why not?

No, these two solvents cannot be used as a solvent pair.

Explanation:

Crystallization: It is a process in which a compound is soluble in liquid from which it is to be solidified as a precipitate.

For crystallization process, the two solvents used should be miscible otherwise, there is no use of using them.

In this case, the solvents given are water and pentane and their miscibility with each other is very far away. Water has very high polarity than pentane.

Therefore, water/pentane system will not work as a solvent pair.

it means there are 3 atoms of oxygen

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.