If a gymnospermic male plant is diploid and female plant is tetraploid, then the ploidy of endosperm will be

The correct option is B Pentaploid

Endosperm forms in the female embryo sac.
If the gymnospermic male is diploid then the pollen will contain 2 haploid male gametes.

If female plant is tetraploid then ploidy of polar nuclei will be diploid.Endosperm develops from fusion of a male gamete and two polar nuclei.
Here the male gamete will be haploid (n).
2 polar nuclei will be diploid (2n).
So the endosperm formed by fusion of male gamete with two polar nuclei will be pentaploid.

Male gamete +2 polar nuclei = Endosperm

(n) (2n) + (2n) (5n)