How are monotremes different from other groups of mammals?

The correct answer will be - they lay eggs

Explanation:

Monotremes are the animals which belong to the group of mammals. There are only five species of monotremes known today which are found in New Guinea and Australia.

The monotremes differ from other mammals which is that they lay eggs instead of giving birth to the young ones. This shows that these mammals are closely related to the reptiles and amphibians and are thus the primitive mammals.

Thus, they lay eggs is the correct answer.