Question

What is the function of a whales tail

Answer 1

The whales tail which is called fluke are used for swimming and also used when they stick their tail out of the water into the air, swing it around, and the slap it on the water's surface. 

Answer 2

A whale's tail is called its flukes. The flukes are used in swimming. Flukes are also used in lobtailing, an activity in which some whales stick their tail out of the water into the air, swing it around, and then slap it on the water's surface.