Introduction:
The question asks to identify the egg-laying mammal out of the given options. The correct answer is option 'B', which is the Platypus.

Explanation:
The platypus is a unique and fascinating mammal native to Australia. It belongs to the monotreme group of mammals, which are characterized by laying eggs instead of giving birth to live young. Here is an explanation of why the platypus is the correct answer:

Monotremes:
Monotremes are a primitive group of mammals that lay eggs. They are the only group of mammals to do so. There are only five extant species of monotremes, and the platypus is one of them.

Physical characteristics:
The platypus has several unique physical characteristics that distinguish it from other mammals. It has a duck-like bill, webbed feet, and a beaver-like tail. The male platypus has venomous spurs on its hind legs.

Egg-laying:
One of the most remarkable features of the platypus is its ability to lay eggs. Female platypuses lay one to three eggs at a time. These eggs are small, leathery, and about the size of a marble. The eggs are incubated in a nest that the female constructs.

Milk production:
After the eggs are laid, the female platypus incubates them by keeping them warm with her body. Once the eggs hatch, the female produces milk to feed the young. However, the platypus does not have nipples like other mammals. Instead, milk is secreted through special glands in the skin, and the young lap it up.

Conclusion:
In conclusion, the correct answer to the question is option 'B', which is the Platypus. This unique mammal is known for its ability to lay eggs, making it one of the few species of egg-laying mammals in the world. The platypus is a fascinating creature with several distinctive physical characteristics, making it a truly remarkable species.