Which of the following lay eggs?
i. Platypus and Echidna
ii. Humans
iii. None of the above

Hint: Egg laying organisms are oviparous and organisms, which produce young ones directly without eggs are viviparous. Platypus and Echidna are the world’s only egg laying mammals or monotremes. They belong to the class mammalia. They live in the burrows on the banks of streams and rivers. There are two species of Echidna that exist. One is present in the highlands of New Guinea. The other is present in Australia.

Complete answer:
Option i. Platypus and Echidna: They are primitive animals with both reptilian and mammalian features. Like reptiles, they lay eggs, have cloaca, single opening for passing urine, sperms or faeces.
Like mammals, they are warm-blooded animals. They nourish and take care of young ones.
Echidnas possess sharp spines, which cover the back part. They have short and stocky bodies. Platypuses possess thick brown fur, which aids in trapping air next to the skin. Bill of platypus looks like a duck. It is venomous in nature. The spur is capable of transferring venom, which is able to cause severe pain in the human body.
The eggs usually hatch between \[10 - 15\] days. They possess a characteristic feature, in which they are able to sense a prey through electro location, which means sensing through electrical signals.
Option i is correct
Option ii. Humans: Humans are viviparous. They are born as live young individuals. They develop into young animals inside the mother.
Hence, Option ii is not correct
Option iii. None of the above: As option i is correct, this option is improbable.
So, Option iii is not correct

Hence, option i. is the correct answer.

Note:
Monotremes come under subclass Holotheria. Echidnas are spiny anteaters or Tachyglossus. The short-beaked echidna is the predominant species. They have a high metabolic rate. They belong to the phylum Chordata and come under subclass Prototheria. They belong to the order Monotremata. Mammals have unique features, which is the presence of mammary glands, through which young ones are nourished by milk.