Which of the following are pyrimidines?

Watson and Crick proposed the model of $DNA$ structure in .......

Thymine is which type of nitrogenous base?

Identify the correct matching for Euchromatin and Heterochromatin from the given statements:
$I -$ Loosely packed
$II -$ Densely packed
$III -$ Darkly stained region
$IV -$ Lightly stained region
$V -$ Transcriptionally active chromatin
$VI -$ Transcriptionally inactive chromatin
Euchromatin $\quad\quad$ Heterochromatin

The two strands of $DNA$ are held together by

The backbone of the $DNA$ molecule is composed of which of the following?