The hydration energy of $Mg^{2+}$ is

Solvay process is used in the manufacture of

Which of the following statements is incorrect?

Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$ :- Sodium is about $30$ times as abundant as potassium in the oceans.
Reason $R$ :- Potassium is bigger in size than sodium.
In the light of the above statements,choose the correct answer from the options given below:

Why is $Li_{2}CO_{3}$ decomposed at a lower temperature whereas $Na_{2}CO_{3}$ at a higher temperature?

Which of the alkali metal chloride $(MCl)$ forms its dihydrate salt $(MCl.2H_2O)$ easily?