the lattice energies of rubudium fluoride RbF and caseium chloride,CsCl are -760kj/mol and -650kj/mol respectively.what is lattice energy of caesium fluoride CsF likely to be

option are

a:-620kj/mol

b:-720kj/mol

c:-800kj/mol

d:-900kj/mol

its answer is b,plz explain me how we will do this

thanks