Tadpoles are young ones of the following

The correct answer is Frogs.

• Tadpoles are the young of amphibians particularly of frogs and toads.
• Fish are aquatic animals.
• The scientific name of Polar bears is Ursus maritimus.
• Torpedo is the underwater ranged weapon launched above or below the water surface through submarines.

Additional Information

• The process by which a tadpole develops into an adult frog is called Metamorphosis.
• A frog lays eggs which become tadpoles in just a few days.
• These tadpoles live underwater and in the next few weeks.
• Hormone thyroxine present in the thyroid gland of the tadpole initiates the process of Metamorphosis.
• Thyroxin hormone produces by the thyroid gland in the presence of Iodine.
• That’s why Iodine should be available in sufficient quantity in the water of the pond.
• If iodine is not available in the diet, then the thyroid may produce an insufficient hormone which will affect the process of metamorphosis. 
• If water is iodine-deficient, in which the frog lays an egg, then tadpoles hatched from these eggs will not grow into adult frogs.