Answer :
The decreasing order of lattice energy realesed is GaN>CaS>LICI>RbBr.
The lattice energy depends on the following two factors. They are product of charges of the compound and radius of the ions.
Higher the charge of ions, higher will be the lattice energy. Smaller the radius of ion, larger will be the lattice energy.
Consider the given compounds as follows: LiCl, CaS, GaN and RbBr
The charges of ions of given compounds are Li⁺, Cl⁻, Ca²⁺, S²⁻, Ga³⁺,N³, Rb⁺ and Br⁻. So, in the given compounds GaN has higher lattice energy. After GaN, CaS has higher lattice energy. Out of two compounds LiCl and RbBr, Li has less ionic well as ionic radius than Rb. Since in groups from top top to bottom atomic size increases as well as ionic radius.
Therefore, LiCl has higher lattice energy than RbBr.
Hence, the decreasing order of lattice energy realesed is GaN> CaS>LICI>RbBr
Learn more about lattice energy from the link given below.
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