During meiosis, a microspore mother cells has 12 bivalents, the number of chromosomes in its pollen grains will be :

The complex formed by a pair of synapsed homologous chromosomes is called a bivalent or a tetrad. Therefore number of bivalent is half the number of chromosome present in the diploid organism. Hence, if the number of bivalent is 12 then the number of chromosomes in its pollen grain will also be 12.