Question

why do tadpoles growing in iodine deficient water fail to grow into frogs

Answer 1

for the metamorphosis i.e. growth of tadpoles..
iodine is required...
so..due to deficiency of iodine....tadpoles fail to grow in frog

Answer 2

Beacause the harmone thyroxine produced by the thyroid gland of the frog is essential to carry out this process of metamorphosis. Iodine is needed for the production of thyroxine;it is made available in which the tadpoles are growing.