Hint: Ionic bonds are formed by complete transfer of electrons and covalent bonds are formed by sharing of electrons. The force between ionic bonds is electrostatic force, while that in covalent bond is Van der Waals force.
Complete answer: Generally, ionic bonds are much stronger than covalent bonds. In ionic bonds, there is complete transfer of electrons between elements to form a stable compound. While in covalent bond, there is only sharing of electrons between two elements to form a stable compound. The force that keeps the ions together is electrostatic force and the force that keeps the elements together bonded with covalent bond is Van Der Waals force. As there is complete transfer of electrons in ionic bonds, cations and anions are formed. Thus there exists a huge electrostatic force of attraction between these ions. As there is only sharing of electrons in elements with covalent bonds, the Van Der Waal’s force existing between them is not as strong as electrostatic force. Ionic compounds also have higher melting and boiling points than covalent compounds, this proves that ionic compounds are stronger than covalent compounds. This is true in general, but there are exceptions where covalent bonds are stronger. The measure of energy to break the bond between elements can be used to determine which bond is stronger. Ionic bonds require more energy to get broken and covalent bonds require lesser energy. However it cannot be said definitively that ionic bonds are stronger than covalent bonds because it depends on a lot of factors. For example, diamonds have a carbon structure in which there are covalent bonds. Diamond is considered as the hardest natural occurring substance on earth.
Note: Ionic bonds are much stronger than covalent bonds in a general sense, but in certain conditions it can happen that covalent bonds become stronger than ionic bonds. So, if conditions are given, you have to look out whether the covalent bond is stronger or an ionic bond.