The correct option is C 25
An immature anther consists of a group of compactly arranged homogenous cells called the sporogenous tissue.
As the anther develops, cells of the sporogenous tissue undergoes meiosis to form microspore tetrads. Hence each cell of the sporogenous tissue is a potential microspore mother cell (MMC)/ pollen mother cell (PMC).
As the anthers mature, the microspores dissociate from each other and develop into pollen grains.
4 pollen grains are formed from 1 MMC (or PMC), so 100 pollen grains are formed from 100/4 = 25 MMC (or PMC).