Question

Which one of the following mammals lays eggs?
A. Kangaroo
B. Ichthyophis
C. Platypus
D. Manatus

Answer 1

Hint: Mammalian subclass Prototheria is historically referred to as monotremes. The only remaining specimens of monotremes are both endemic to Australia and New Guinea, although there is proof that they have once again been widespread in South America with some extinct populations.

Complete answer
The monotremes are distinguished by anatomical variations in their heads, mouths, digestive tract, reproductive organs and other areas of the body relative to the more typical forms of mammals. Existing monotremes as adults lack the jaw. Young fossil shapes and modern platypus have a "tribosphenic" molar pattern that is one of the defining characteristics of current mammals
From the given options,
>The kangaroo is a marsupial animal that gives birth to its young one. They have pouches on the abdomen to carry their young.
>Ichthyophis is a genus of caecilians, a worm like amphibian.
>The platypus, also known as the Ornithorhynchus or duck-billed platypus, is a monotreme semi-aquatic egg-laying mammal and is native to eastern Australia.Like all other mammals, monotremes are endothermic with a strong digestion rate; have fur on their bodies; develop milk from mammary glands to feed their babies; have one single bone in their bottom jaw; and also have three middle-ear bones.
>Manatus Is a large aquatic mammal that gives birth to one or two calves every two years.

Thus, the correct option is option C i.e. Platypus.

Note: The Monotreme jaws are built somewhat differently than those of other animals, and the muscle that opens the jaw is distinct.Some monotremes do not have teeth but have an extra set of bones on shoulder.