What is the backbone of the DNA Chain composed of

A sugar-phosphate-sugar chain.

Explanation:

A sugar-phosphate-sugar chain forms the "backbone" of DNA. Nitrogenous bases are faced inside. Within a polynucleotide chain, the two nucleotides linked together by a bond, which is called a phosphodiester bond. In nucleotide, phosphoric acid and pentose sugar (deoxyribose) are bonded with phosphoester bond. And pentose sugar and nitrogenous bases are bonded with the N-Glycosidic bond. The two strands of DNA are held together by Hydrogen bonds, which present between nitrogenous bases of the opposing strand.