The length of DNA in one chromosome is 510A⁰. It has 20% of 6 -aminopurines. The total  number of nucleotides and hydrogen bonds in that chromosome respectively, are

6 – aminopurine = Adenine

If adinies are 20% then thymidine will be 20% so remaining 60% will be equally shared by guanine and cytocine so each 30%

34 Å= 20 nucleotides

510 Å = ?

20/34 × 510 = 300 nucleotides

In that 20% is adenine so there are 60 adinies

Hydrogen bonds = 60×2 =120

30 persent are guanine so there are 90 guanine nucleotide

Hydrogen bonds 90×3=270

So total hydrogen bonds are

270+120=390