To which of the taxonomic group does whale belong?

The zygomatic arch in the skull of a mammal $(rabbit)$ is formed by:

Assertion : The duck-billed Platypus and the spiny ant-eater,both are egg-laying animals yet they are grouped under mammals.
Reason : Both of them have seven cervical vertebrae and $12$ pairs of cranial nerves.

Hairs occur in all mammals except those of

Which of the following is a flying mammal?

Which characteristic is found exclusively in mammals?