"Where are Euchromatin and Heterchromatin found?"
– Everywhere…

"Is either Euchromatin or Heterochromatin found in the mitochondrial genome?"
– Both.

Euchromatin – is actively transcribed portion
Heterchromatin – inactive, packed portion
Most of the time majority of chromosomes will be representatives of both states.

So the chromosomes attain both active and inactive stages… Thats what you mean to say

Well Qutub, i dont think that is what Cat means to say. Its not an issue of stages of the chromosome, but regions of each chromosome. But yes, regions of any eukaryotic chromosome can be either open or closed. Another issue, perhaps to which you refer is that chromosomes pass through active and inactive stages could refer to stages of cell division when the chromosomes change state in preparation for cell division. But thats different.