• Assertion (A) is True: In the angiosperm female gametophyte (embryo sac), the large diploid/dikaryotic central cell is functionally a female gamete alongside the haploid egg cell.
• Reason (R) is True & Explains (A): In double fertilization, one sperm cell fertilizes the egg cell to form the diploid zygote ($2n$), while the second sperm cell fuses with the central cell (containing two polar nuclei) to form the triploid ($3n$) primary endosperm nucleus.
• Conclusion: Both (A) and (R) are true and (R) is the correct explanation of (A).

Correct option: (1) Both (A) and (R) are true and (R) is the correct explanation of (A)