A double-stranded DNA of $1000$ base pairs (2000 bases in all) has $30%$ adenine of the total bases. Taking A-T = 2 and G-C = 3 hydrogen bonds per pair, the total number of hydrogen bonds is

Answer: A

A = 600, so T = 600 by Chargaff. G + C = 800, so G = C = 400. A-T pairs: 600, G-C pairs: 400. Hydrogen bonds =

600 \times 2 + 400 \times 3 = 1200 + 1200 = 2400