The correct option is D 50
Megaspore mother cell first undergoes one round of meiotic division forming four haploid megaspores. Out of these four megaspores, three gets degenerated and gradually disappear. Only one functional megaspore remains, which undergo mitotic divisions to form an 8-nuclei and 7-celled structure.
So, to form one functional megaspore one round of meiosis is required. Hence, 50 functional megaspores will require 50 meiotic divisiona.