Question 1 for AQA C2 Answer

The high melting point of sodium chloride is due to the strong electrostatic attraction between the Na⁺ ion and the Cl^- ion.

Extra information:  The ions are formed by an electron being removed from a sodium atom and the chlorine atom gaining an electron. Although energy is needed to remove an electron from the sodium atom this is small in comparison to the energy released by forming the chloride ion and the large amount of energy released by the ions sticking together.