A DNA molecule has 100 bp. The number of adenine residues in it is 40. Calculate the total number of hydrogen bonds present in the DNA.

DNA molecule has 100bp= 200 nucleotides.
No. of adenine residues= 40
Therefore, no. of thymine residues= 40
Total no. of guanine and cytosine present= 200-(40+40) = 120
No. of cytosine= No. of guanine= 120/2= 60
2 hydrogen bonds between A and T and 3 hydrogen bonds between G and C
Total no. of hydrogen bond= (60*3) + (40*2) = 260