What is the full form of $PEN$?

The fusion of male and female gametes is called:

Fusion of egg and male gamete $- P$
Fusion of secondary nuclei and male gamete $- Q$
Select the correct option for $P$ and $Q$.
$\quad\quad P \quad\quad\quad Q$

Define/Explain: Double Fertilisation.

In angiosperms,triple fusion is required for the formation of which of the following?

What is the function of the two male gametes produced by each pollen grain in angiosperms?