Which of the following substances has the highest melting point?

The correct solubility order is:

Which of the following compounds is the least ionic?

In the formation of $NaCl$ from $Na$ and $Cl$,which of the following occurs?

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 $NaBr_{(s)}$ $= -360.1 \ kJ \ mol^{-1}$.

$HCl$ gas is covalent and $NaCl$ is an ionic compound. This is because