The pollen grain is
An immature male gametophyte
A mature male gametophyte
Partially developed male gametophyte
Last stage of male gametophyte
$A$ : The generative cell comes to lie freely in the cytoplasm of the tube cell.
$R$ : Cellulosic wall around generative cell is dissolved.
How many meiotic divisions are necessary to produce $100$ pollen grains
Endothecium layer of anther lobes is present