For a salt $\mathrm{MX}(\mathrm{s})$ the lattice enthalpy (energy needed to separate the solid into gaseous ions) is $+758\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$, and the hydration enthalpies of the gaseous ions are $-406$ for $\mathrm{M}{}^{+}$ and $-364\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ for $\mathrm{X}{}^{-}$. The enthalpy of solution of $\mathrm{MX}$ and the temperature change on dissolving it in water are

1. A$+12\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$; the solution warms
2. B$-12\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$; the solution cools
3. C$-12\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$; the solution warms
4. D$-1528\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$; the solution warms