Which two nitrogenous bases are of the purine type?

Which of the following base pairs is incorrect?

Which of the following statements is incorrect regarding the $DNA$ model proposed by Watson and Crick?

What structure is formed when two polynucleotide chains in $DNA$ are coiled together?

Distinguish between: Repetitive $DNA$ and Satellite $DNA$.

Which of the following statements are correct with reference to the packaging of the $DNA$ helix?
$(A)$ Histones are organized to form a unit of eight molecules called a histone octamer.
$(B)$ Histones are negatively charged basic proteins.
$(C)$ Histones are rich in the basic amino acid residues - lysine and arginine.
$(D)$ The negatively charged $DNA$ is wrapped around the positively charged histone octamer to form a nucleosome.
$(E)$ The packaging of chromatin at higher levels requires an additional set of proteins called non-histone chromosomal proteins.