Question

what are the \bars\ connecting the backbone of dna? salt and phosphates air and phosphates nitrogenous bases water and phosphates

Explanation:

DNA's structure has a backbone of sugar - phosphate, and the "bars" connecting the two strands of the backbone are nitrogenous bases (adenine - thymine, guanine - cytosine pairs). Salt, air, or water are not the connecting "bars" here.

Answer:

Nitrogenous bases