The melting points of ionic compounds 1. are very low because ionic bonds are very weak 2. are very high because ionic bonds are very strong 3. are very low because they are liquids at room temperature4. have no relation to the strength of the ionic bonds

The melting points of ionic compounds are very high because ionic bonds are very strong. Ionic bonds are strong because they are held together by strong electrostatic force. In order to break the bonds, a lot of energy is needed. The ions charge and size affect their melting points. 

Ionic compounds are hard, brittle, have high boiling points and are insulators. 

Ray 2 should cross through the focal point on the right side of the lens

The answer is n = 2  and    n = 3