Which of the following is a purine derivative?

Which carbon atom of deoxyribose sugar in $DNA$ does $NOT$ contain the $-OH$ group?

In a nucleotide,the phosphate linkage is generally attached to -

$RNA$ and $DNA$ are chiral molecules. Their chirality is due to the presence of:

The total number of hydrogen bonds in a $DNA$ double helix strand,where one strand has the following sequence of bases,is $...........$
$5^{\prime}-G-G-C-A-A-A-T-C-G-G-C-T-A-3^{\prime}$

The number of complementary hydrogen bond$(s)$ between a guanine and cytosine pair is