Obviously its in a back bone or vertebrae those the terms vertebrates and invertebrates which means without a back bone
Yes
Yes they are - they have a complete skeleton including skull, ribs and spine.
Yes, reptile have vertebrae. Snakes have especially distinctive vertebrae as they are the only animal to have a zygosphene and zygantrum, to keep the adjacent vertebrae from twisting. Turtles are also distinctive as most are fused to the carapace.
No, fish are vertebrates.Yes fish have backbones, at least in general. I'm sure there is some freak of nature that doesn't follow the rules. There always is.