What forms the backbone of a polynucleotide chain?

Step-by-step solution

The salient features of the Double-helix structure of DNA are as follows: (i) It is made of two polynucleotide chains, where the backbone is constituted by sugar-phosphate, and the bases project inside . (ii) The two chains have antiparallel polarity. It means, if one chain has the polarity 5'🡪3', the other has 3’🡪5'. (iii) The bases in two strands are paired through hydrogen bond (H-bonds) forming base pairs (bp). Adenine forms two hydrogen bonds with Thymine from opposite strands and vice-versa. Similarly, Guanin