Two segments of dna have the exact same number of each nucleotide. do they necessarily code for the same protein?

No because the order of the different nucleotides may be different in which means that the order of the amino acids may be different and thus leading to different proteins.

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds