I agree with Tara. It does sound confusing. Maybe you are supposed to be talking about a "rack of back ribs." Back ribs is a section of meat and bone that the butcher cuts from the pig right next to the spine of the pig. The ribs stay together in a row of many ribs (8 to 12 ribs together |||||||||||| like piano keys). The row is called a "rack" of ribs. The best meat is on the small ribs next to the lower part of the spine. These ribs are smaller then the ribs at the chest. These smaller ribs are called "baby back" ribs. If this is what you are trying to say, then the phrase would be, "I just bought one kilogram of pork back ribs to cook." bon appetit. :-)

vertebrae is a term that used mostly in formal discourses on subjects like anatomy. Spine is probably the most common, but backbone would work as well. Also, ew, I've never heard of eating pork backbone before (how do you even eat "bone?")