Assertion: $\mathrm{BeSO}_4$ is soluble in water while $\mathrm{BaSO}_4$ is not. Reason : Hydration energy decreases down the group from $\mathrm{Be}$ to $\mathrm{Ba}$ and lattice energy remains almost constant.

• Correct answer
  A

  If both assertion and reason are true and reason is the correct explanation of assertion.
• B

  Ifboth assertion and reason are true but reason is not the correct explanation of assertion.
• C

  If assertion is true but reason is false.
• D

  If both assertion and reason are false.

Hence, the correct answer is option: 'A'.