Can a platypus bite

No. To begin with, platypuses have no teeth so they cannot bite.

However, the male platypus does have the distinction of being one of the world's most venomous mammals. This creature has a small, hollow, poisonous spur on the back of each of its hind feet. The venom cannot kill a person, but it will cause swelling and excruciating pain that can last for months. The venom is enough to kill an animal the size of a small dog, but not a healthy human.