Answer: The order of increasing lattice energy is [tex]Li_2S>K_2S>Rb_2S[/tex]
Explanation: Lattice energy is defined as the energy required to break the intermolecular force that is responsible for the formation of a lattice.
Melting point is defined as the temperature at which solid gets converted into liquid due to the weakening of the bonds in the solid form.
The relationship between these two is direct.
[tex]\text{Lattice energy}\propto \text{Melting point}[/tex]
More the melting point of a compound, more will be its lattice energy.
Order of increasing Lattice energy will be:
[tex]Li_2S>K_2S>Rb_2S[/tex]
