Chemistry of the phosphodiester bond in RNA
Generally hydrogen is not shown in DNA structure. I have made a simple diagram to show where all hydrogens go:



There are 3 hydrogens in phosphoric acid, each of them leaves as:


1 H joins with 3' -OH of previous nucleotide to form H2O during DNA replication.
1 OH joins with H of next nucleotide to form H2O during DNA replication.
1 H is released as H+ (remember it was phosphoric acid), hence giving rise to the acidic character of DNA (remember it is DeoxyriboNucleic Acid).


I think you should first study DNA replication (if you haven't, yet) to get more thorough knowledge about the topic.