A lion is a mammal because it has fur that covers it's body, it feeds it's young with milk which is produced by the mother, it is warm blooded and it gives birth like a human would. Not by laying eggs. A reptile does lay eggs. The eggs are hard and leathery, it has scaly dry skin and is cold blooded. It has no fur on it's body and does not feed it's young with milk.
A lion is a mammal because it has fur and hair and it feed it young milk produced in the mother's body, and are warm--blooded. And a reptile live in the water and the land that why a lion can't be a reptile because reptile shade they skin and lions don't shade their skin.
A lion is a mammal. Mammals are warm blooded and have fur/feathers. Reptiles are cold blooded and have scales/fins.
Mammals are animals that have hair/fur, bear live young (with one or two exceptions), feed their young with milk produced in the mother's body, and are warm-blooded. Reptiles are cold-blooded, have scales, mostly lay eggs instead of giving birth to live young (again, there are exceptions), and the mothers don't produce milk for their young. Which of these sounds like a lion to you?
Mammal
A lion is a mammal