Final answer:
Iodine deficiency is the leading cause of preventable mental impairment worldwide, crucially impacting cognitive function during early development.
The correct option is b.
Step-by-step explanation:
The leading cause of preventable mental impairment worldwide is b) Iodine deficiency. Iodine is crucial for thyroid hormone production, which is essential for normal brain growth and development from the fetal stage through early childhood. A severe lack of iodine during these critical periods can cause permanent intellectual disability.
In children, extreme iodine deficiency can even lead to cretinism, a severe form of stunted growth and mental development. Unlike other micronutrient deficiencies that primarily affect physical health, such as iron deficiency which causes anemia, iodine deficiency has a significant impact on cognitive function and is the most crucial factor in preventable intellectual disability globally.
The correct option is b.