The reason for decreasing solubility of alkaline earth metal carbonates and sulphates down the group is

$\mathrm{increase} \mathrm{in} \mathrm{lattice} \mathrm{enthalpy} \mathrm{and} \mathrm{decrease} \mathrm{in} \mathrm{hydration} \mathrm{enthalpy}$

$\mathrm{constancy} \mathrm{in} \mathrm{lattice} \mathrm{enthalpy} \mathrm{and} \mathrm{decrease} \mathrm{in} \mathrm{hydration} \mathrm{enthalpy}$

$\mathrm{decrease} \mathrm{in} \mathrm{lattice} \mathrm{enthalpy} \mathrm{and} \mathrm{constancy} \mathrm{in} \mathrm{hydration} \mathrm{enthalpy}$

$\mathrm{decrease} \mathrm{in} \mathrm{both} \mathrm{lattice} \mathrm{enthalpy} \mathrm{and} \mathrm{hydration} \mathrm{enthalpy}$