Answer: [tex]Rb_2S[/tex] < [tex]K_2S[/tex] < [tex]Li_2S[/tex]
Explanation:
Lattice energy is the energy required to dissociate 1 mole of the an ionic compound into its constituent ions.
Thus higher is the lattice energy more energy will be required to melt the compounds.
As [tex]Li_2S[/tex] has highest melting point, it will require most energy to melt an hence it will have highest lattice energy. The order of three compounds in order of increasing lattice energy
[tex]Rb_2S[/tex] < [tex]K_2S[/tex] < [tex]Li_2S[/tex]
