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I think you left a little info out of the question. For some purposes (like being replicated or transcribed) DNA cannot be in chromosome form. For other purposes (like being transported during cell division) it must be in chromosome form.
I think you're asking about the state DNA has to be in to be visualized? If you are, then it must be packaged into chromosomes to be stained and visible with a plain light microscope (unwound DNA is visible with much more powerful electron microscopes). The cell only wraps DNA up into chromosomes when it's dividing (or getting ready to divide) so to see it, you'd have to look at cells which are dividing as opposed to cells which are not.
But what is G0?
G0 just mean the cell isn't a dividing cell. It has 'left' the cell cycle, so to speak.
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You can visualise dna in chromosome form in pachytene phase in case of small chr. if chromosomes are large you can go for metaphase. In Go you can not see the chromosome since it is in highly decondensed form.