Assertion : $\mathrm{Na}_2 \mathrm{SO}_4$ is soluble in water while $\mathrm{BaSO}_4$ is not. Reason :…
Assertion : $\mathrm{Na}_2 \mathrm{SO}_4$ is soluble in water while $\mathrm{BaSO}_4$ is not.
Reason : Lattice energy of $\mathrm{BaSO}_4$ exceeds its hydration energy.
If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
If Assertion is true but Reason is false.
If Assertion is false but Reason is true.
Solution
The large sized sulphate anion $\left(\mathrm{SO}_4{ }^{2-}\right)$ is stabilised better by a large sized cation. So the stability of sulphates down the group increases so the lattice energy is more in $\mathrm{BaSO}_4$ than in $\mathrm{Na}_2 \mathrm{SO}_4$.