The correct answer is Option D: A-III, B-IV, C-I, D-II

Here's a breakdown of why:

Histones (A) - Positively charged basic proteins (III)

Histones are proteins that are rich in basic amino acids (like lysine and arginine), giving them a positive charge. This positive charge allows them to bind tightly to the negatively charged DNA molecule.

Nucleosome (B) - DNA wrapped around histone octamer (IV)

A nucleosome is the fundamental unit of chromatin. It consists of a core of eight histone proteins (two each of H2A, H2B, H3, and H4) around which a segment of DNA is wrapped. This wrapping is what gives chromatin its "beads-on-a-string" appearance.

Euchromatin (C) - Loosely packed chromatin (I)

Euchromatin is a less condensed form of chromatin that is actively transcribed. It is more loosely packed, allowing access for transcription factors and other proteins involved in gene expression.

Heterochromatin (D) - Densely packed chromatin (II)

Heterochromatin is a highly condensed form of chromatin that is generally inactive in transcription. It is densely packed, making it difficult for transcription factors to access the DNA.

Therefore, the correct match is:

A - III

B - IV

C - I

D - II