The alkaline earth metal sulphate(s) which are readily soluble in water is/are :
A. BeSO₄
B. MgSO₄
C. CaSO₄
D. SrSO₄
E. BaSO₄
Choose the correct answer from the options given below :

Solution

Chemistry ma’am · 4 steps

Sulphate is so big that lattice energy hardly changes; the cation's hydration energy decides it all.

1. Two competing energies. A salt dissolves when the energy released by hydrating its ions is large enough to pay for breaking the lattice. Here the anion is always SO₄²⁻.
2. Lattice energy stays flat. SO₄²⁻ is a large anion, so changing the small cation barely changes the cation–anion distance. The lattice energy stays almost the same from Be to Ba.
3. Hydration energy falls. Hydration energy depends strongly on cation size. It is very high for the tiny Be²⁺ and Mg²⁺, and it drops sharply as the cation grows down the group. So solubility falls down the group.

   Sulphate	Cation size	Hydration energy	Solubility in water
   BeSO₄	smallest	very high	readily soluble
   MgSO₄	small	high	readily soluble (Epsom salt)
   CaSO₄	medium	lower	sparingly soluble
   SrSO₄	large	low	nearly insoluble
   BaSO₄	largest	lowest	insoluble

4. So. Only BeSO₄ and MgSO₄ are readily soluble, which is option (a), A and B.

The idea to keep. With a big anion like sulphate, lattice energy is nearly constant, so the cation's hydration energy sets the trend. Small cation means high hydration and high solubility, so solubility falls down the group.

Answer from the NTA final answer key. Solution by PrepWiser.