Find the length of the DNA having 450 hydrogen bonds and 90 adenine residues.

No. of adenine= No. of thymine= 90
Total no. hydrogen bonds between A and T= 90*2=180
Total no. of hydrogen bonds between G and C= 450-180= 270
No. of G and C= 270/3= 90
Total no. of base pairs= 90+90=180 bp
Let the length of the DNA be x.
(x/34)*10= 180
x= 612 $\stackrel{0}{\mathrm{A}}$