A diploid organism havenig one chromosome less or having one unpiared chromosome in the body is called monosomy.
If the n=x , then the diploid set will be 2x (2n).
Such a diploid cell , if it has monosomy , then it should be (2n-1).
In a human diploid cell, monosomy is 46-1=45 chromosomes.
If the cell is hexaploid and if it is in monosomy , then 6x-5 will be the monosomy.Where one chromosome is represented only once.