Ionic compounds are formed most easily with

An ionic bond $P^{+} Q^{-}$ is most likely to be formed when

The melting point of $RbBr$ is $682\,^{\circ}C$ while that of $NaF$ is $988\,^{\circ}C$. The principal reason for this fact is

Use the following data to calculate $\Delta _{lattice}H^{\theta }$ for $NaBr$. $\Delta _{sub}H^{\theta }$ for sodium metal $= 108.4 \ kJ \ mol^{-1}$,ionization enthalpy of sodium $= 496 \ kJ \ mol^{-1}$,electron gain enthalpy of bromine $= -325 \ kJ \ mol^{-1}$,bond dissociation enthalpy of bromine $= 192 \ kJ \ mol^{-1}$,$\Delta _{f}H^{\theta }$ for $NaBr_{(s)}$ $= -360.1 \ kJ \ mol^{-1}$.

Which of the following is an electrovalent linkage?

The compound in which the cation is isoelectronic with the anion is