Is sodium nitrate a covalent or ionic compound? This is a test question. I put the answer ionic compound but my teacher says that statement is false because it is only partially ionic as there is covalent bond between nitrogen and oxygen in the nitrate ion. Is that true?
Bonds are usually used to describe how electrons are shared. "Partially ionic bonds" are polar covalent bonds. Which is not the same as saying that a compound has different types of bonds in the whole compound. I think that your teacher gave you a bad question and a bad answer. If the question had asked whether all the bonds in sodium nitrate are ionic, then it would be a different story.
However, it is true that the bonds between the nitrogen and oxygen are covalent. Nevertheless, stating that sodium nitrate is ionic shouldn't be wrong.
If you are asked on a test "Is sodium nitrate ionic or covalent?", say "ionic" and if given the opportunity, justify your answer with electrical conductivity of molten sodium nitrate and aqueous sodium nitrate.
In addition to atomic ions such as Na+ and Cl-, ionic compounds often contain groups of atoms with a net electrical charge. Sodium nitrate is an example of an ionic substance that contains such a group.
The answer your teacher seems to have been looking for was to specify that the the sodium-nitrate bond is ionic and nitrate's nitrogen-oxygen bond is covalent.
This is under the assumption that the question was not multiple choice but was short answer. You may be able to contest the marking, but I wouldn't expect a change.