Question

Red blood cells have no nucleus ,then why do we call them cells?

Answer 1

Initially red blood cells had nucleus..but eventually it was expelled out at the development phase and so they were termed as red blood cells.

Answer 2

Though initially the Red Blood Cells have nucleus but as they get mature they lose their nucleus completely to provide large surface area so that it can carry oxygen to all parts of the body. Hence, they are called so.
Hope this helps you !!