How many polynucleotides are there in one molecule of DNA?
In general, it is right since with the term DNA you commonly refer to the double-stranded DNA. However, you need to be aware that DNA may exist in different forms.

Single-stranded DNA (ssDNA), for example, is composed of only one strand of DNA, so one chain of nucleotides or one polynucleotide molecule.

Double-stranded DNA (dsDNA) is the common form of DNA found in cells and it is composed of two polynucleotide molecules.

Triple-stranded DNA (tsDNA ?) also exist, which of course, is composed of 3 polynucleotide molecules.