A diploid female plants crossed with tetraploid male. The ploidy of endosperm will be
Parents: 2n (Diploid female) × 4n (Tetraploid male)
Gametes: n (Female gamete) × 2n (Male gamete)
The endosperm is formed by the process of triple fusion, wherein one male gamete fuses with the two polar nuclei.
In this case, the two polar nuclei are haploid but the male gamete is diploid (2n). Hence, the endosperm would be tetraploid (n + n + 2n = 4n).
so, option A is correct.