Final answer:
Approximately 90% of all serious defects occur for unknown reasons.
Step-by-step explanation:
The question is asking for the percentage of all serious defects that occur for unknown reasons. To find the answer, we need to refer to the information provided.
In the given information, it states that the global average of all live births complicated by malformation is 6%. The majority of these complications are due to unknown factors. Only 10% of recognized causes are attributed to environmental factors. Based on this information, we can determine that the percentage of all serious defects occurring for unknown reasons is the majority, which is approximately 90%.
Therefore, approximately 90% of all serious defects occur for unknown reasons.