Nitrates are compounds containing nitrate ion. Nitrate ion consisting of one central nitrogen atom surrounded by three oxygen atoms in trigonal planar arrangement. The nitrate ion carries a formal charge of -1. Nitrates are mainly produced for use as fertilizers in agriculture because of their high solubility and biodegradability. Common examples of inorganic nitrate salts are sodium nitrate, potassium nitrate, ammonium nitrate etc. Leafy green foods such as spinach and arugula are rich source of inorganic nitrate.
This video explains how to test the presence of nitrate ion in a given salt.