(c) : Nucleosomes appear as ‘beads­on­string’ in the chromosome when viewed under electron microscope. The beads in ‘beads­on­string’ arrangement are complexes of histones and $DNA$. The bead plus the connecting $DNA$ that leads to the next bead from the nucleosome. Nucleosome is the fundamental unit of organization on which the higher­ order packaging of chromatin is built. The bead of each nucleosome contains eight histone molecules in which two copies each of $H_2A, H_2B, H_3$ and $H_4$ are found.