Here's why:

* DNA is the molecule itself, a long chain of nucleotides.

* Chromosomes are the highly organized structures of DNA that are found within the nucleus of a cell. They consist of the DNA strand coiled and packaged around proteins called histones.

* This coiling and packaging allows the incredibly long DNA molecule to fit inside the nucleus of a cell and be organized for processes like replication and transcription.

So, a very long DNA strand coiled many times containing thousands or millions of nitrogen bases is best described as a chromosome.