Which of the following crystalline ionic compounds has the smallest magnitude of lattice enthalpy, thereby requiring the least energy to fully dissociate one mole of the solid ionic lattice into its constituent gaseous ions?
MgO\text{MgO}MgO
BaO\text{BaO}BaO
LiF\text{LiF}LiF
RbI\text{RbI}RbI