Is one DNA molecule same as one chromosome
Considering the encyclopedic definition of a molecule...  


  Molecules are held together by shared electron pairs, or covalent bonds.


...one DNA molecule is one DNA strand.

Put another way, one DNA molecule is a polymer of nucleotides connected by phosphodiester bonds. This means that one intact double-stranded chromosome is composed of two molecules of DNA interacting by hydrogen bonds.  

In practice, however, one piece of double-stranded DNA is commonly called a DNA molecule.  

All of the chromosomes in a cell constitute a single genome.  

To further add to the confusion, identical chromatids may be said to compose a single chromosome, such that one replicated chromosome composed of two chromatids may comprise four DNA molecules, by the definition outlined above.



Note, the same encyclopedia lists ionic bonds as being on the same "continuum" as covalent bonds...


  Ionic and covalent bonding therefore can be regarded as constituting a continuum rather than as alternatives.


...so atoms held together in ionic interactions are also considered molecules, by this definition.