Question

what is double- fertilization?

Answer 1

Two two male gametes are released in to the ovary.One fuses with the egg to form zygote,process is called syngamy and other fuses with two polar nuclei to for PEN(Primary endosperm nucleus) and process is called triple fusion.As two male gamates are involved in both proces hence it is called double fertilisation.
In general
triple fusion. + syngamy. = Double fertlisation