The nucleus serve as the ?

The nucleus servers as the "Control center" of the cell.

Explanation:

The nucleus is the place where all DNA is held and controls the process of transcription and translation.

Depending on the subject;

The nucleus can also be discribed as the central and most important part of the group, and it forms the the basis for its activity and growth.

I hope this helps! : )

the index of refraction of the second medium is higher. i just took the test trust me !

im not intirely sure but i think the anwser is d relative humidity