Is DNA a single molecule or 46 separate pieces (out of 23 chromosome pairs)?
Unbroken strands of DNA are single molecules. So Yes, DNA is a molecule. However, the sequence of nucleotides allow for a near infinite variety. So unlike other molecules, like collagen, or water, they cannot be characterized with a unique descriptive name, other than by their sequence. I think this is the cause for confusion, because in this sense, DNA is a class of molecules, and we don't generally give them names. Each chromosome has two unique DNA molecules in diploid organisms (except in rare cases of highly inbred individuals where the two molecules might be identical). So if you have 23 chromosomes, you have 46 DNA molecules in each cell nucleus.