For four hypothetical salts the lattice enthalpy (magnitude, energy released when the solid forms from gaseous ions) and the sum of the hydration enthalpies of the ions (magnitude) in $\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$ are: P (2280, 2105), Q (2190, 2168), R (1950, 1970), S (2410, 2300). Which salt has the most exothermic enthalpy of solution, and what is that value?

1. AP, $+175\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
2. BR, $+20\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
3. CQ, $+22\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
4. DR, $-20\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$