Iodine deficiency causes:

Assertion: The thyroid gland is composed of follicles and stromal tissue.
Reason: Iodine is essential for the normal rate of hormone synthesis in the thyroid.

On an educational trip to Uttaranchal,Ketki and her friends observe that many local people have swollen necks. Please help Ketki and her friends to find out the solutions to the following questions.
$(a)$ Which probable disease are these people suffering from?
$(b)$ How is it caused?
$(c)$ What effect does this condition have on pregnancy?

Cretinism can be prevented or cured by the administration of

Metamorphosis in frogs is accelerated by $.....$.

Which substance is responsible for metamorphosis in amphibians?