Question

The correct order of the solubility of alkaline-earth metal sulphates in water is :
A. $Mg<Sr<Ca<Ba$
B. $Mg<Ca<Ba<Sr$
C. $Mg>Sr>Ca>Ba$
D. $Mg>Ca>Sr>Ba$

Answer 1

The alkaline earth metals are all of the elements in the second column (column 2A) of the periodic table. This group includes beryllium ($Be$), magnesium ($Mg$), calcium ($Ca$), strontium ($Sr$), barium ($Ba$) and radium ($Ra$). Alkaline earth metals have only two electrons in their outermost electron layer.

Step by step answer: The solubility of the alkaline earth's metal sulphates in water decreases in the sequence $Mg>Ca>Sr>Ba$.
With the increase in the cationic size on moving down the group, the extent of the hydration of the cation decreases. However, the decrease in the lattice energy with increase in cationic size is small.
Thus, the decrease in hydration energy is more significant than the decrease in lattice energy. Hence, the solubility of the alkaline earth's metal sulphates in water decreases on moving down the group.

Hence, the correct option D. $Mg>Ca>Sr>Ba$.

Additional Information: They are beryllium ($Be$), magnesium ($Mg$), calcium ($Ca$), strontium ($Sr$), barium ($Ba$), and radium ($Ra$). The elements have very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure.

Note: All the alkaline earth metals readily lose their two outermost electrons to form cations with a 2+ charge. All of the alkaline earth metals except magnesium and strontium have at least one naturally occurring radioisotope. Magnesium and calcium are ubiquitous and essential to all known living organisms.