Explanation:
Monotremes are a unique group of mammals that lay eggs instead of giving birth to live young.
They are the only egg-laying mammals and include species like the platypus and echidna.
They also produce milk, but they do not have nipples; instead, milk is secreted through specialized skin glands.
Thus, the defining characteristic of monotremes is that they lay eggs.
Explanation by: Mr. Dubey
Monotremes are a unique group of mammals that lay eggs instead of giving birth to live young.
They are the only egg-laying mammals and include species like the platypus and echidna.
They also produce milk, but they do not have nipples; instead, milk is secreted through specialized skin glands.
Thus, the defining characteristic of monotremes is that they lay eggs.