Final answer:
An oogonium with 46 chromosomes would produce an ovum with 23 chromosomes.
Step-by-step explanation:
An oogonium is an immature egg cell that undergoes cell division to produce an ovum. In humans, an oogonium has a diploid number of chromosomes, which is 46. During oogenesis, the primary oocyte, formed from the oogonium, goes through the first cell division of meiosis, reducing the chromosome number by half. Therefore, an ovum produced from an oogonium with 46 chromosomes would have 23 chromosomes, not 18.