During formation of pollen grains, a microspore mother cell undergoes

The correct option is A One meiotic division

• Pollen grains are formed from the microspore mother cell by the process of microsporogenesis and microgametogenesis.
  
• Microsporogenesis is the formation of haploid microspores from diploid microspore mother cells through meiosis. Microgametogenesis is the development of microspore into mature pollen grains.
  
• Hence, during the formation of pollen grains, microspore mother cell undergoes one meiotic division to produce four haploid microspores, generally in the form of a tetrad, which then develops into pollen grains.
  

So, the correct answer is A.