Which of the following nitrogenous bases is not found in $DNA$?

Histones are enriched with $-$

In which of the following are split genes found?

The number of $H$-bonds between Guanine and Cytosine is .....

Read the following statements and choose the set of correct statements:
$(a)$ Euchromatin stains light.
$(b)$ Heterochromatin is transcriptionally inactive.
$(c)$ Histone octamer contains eight molecules of histone proteins.
$(d)$ Packaging of chromatin at higher level requires additional set of proteins that are referred to as non-histone chromosomal $(NHC)$ proteins.
$(e)$ In a human diploid cell,$6.6 \times 10^9$ base pairs are present,not $6.6 \times 10$ nucleosomes.
Choose the correct answer from the options given below:

The minimum requirement for a mutation is a change in: