Hello dear student,

I understand your query but you need to tell about which endosperm you are talking about here if it's human or gymnosperms or angiosperms or some other plant . But nevertheless less

The ploidy of gymnosperms endosperm is n that is haploid  that is it is made up of haploid chromosome.

The ploidy of angiosperm endosperm is 3n that is triploid .

I hope this helps . Thank you and best wishes