Answer: 3) potassium nitrate
Explanation:
An ionic bond is formed when an element completely transfers its valence electron to another element. The element which donates the electron is known as electropositive element and forms a positively charged ion called as cation. The element which accepts the electrons is known as electronegative element and forms a negatively charged ion called as anion.
A covalent bond is formed when an element shares its valence electron with another element. This bond is formed between two non metals.
1. potassium chloride : is made up of ionic bond between metal and non metal.
2. potassium hydride : is made up of ionic bond between metal and non metal.
3) potassium nitrate : made up of ionic bond and is made up of covalent bond between two non metals nitrogen and oxygen.
4) potassium oxide: is made up of ionic bond between metal and non metal.
Thus potassium nitrate contains both ionic and covalent bonds.