Error

34 Angstrom = 10 base pairs, so 68 Angstrom = 20 base pairs.

(i) 40% A=T bps. So, 8 A=T bps as total is 20(from above) and remaining 12 G=C bps.

A=T Hydrogen bond; A=T bps * 2 = 16;

G=C Hydrogen Bond; G=C bps * 3 = 36.

So total Hydrogen bond=52

(ii) 20 bps means one strand DNA has 20 nucleotide. Between adjacent nucleotide, one phosphodiester bond is present. So, 20 adjacent nucleotide will have 19 phosphodiester bonds. Equal number of phosphodiester bond on other strand. Therefore, total = 19 * 2 =38

(iii) Between sugar and base(part of every nucleotide), there is one glycosidic bond. Therefore, total = 20 * 2 = 40.