Glauber's salt is

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

Which of the following reactions does not liberate a gaseous product?

Oxygen gas can be prepared from solid $KMnO_4$ by

Given below are two statements:
Statement $I$: The chlorides of $Be$ and $Al$ have $Cl^{-}$-bridged structure. Both are soluble in organic solvents and act as Lewis acids.
Statement $II$: Hydroxides of $Be$ and $Al$ dissolve in excess alkali to give beryllate and aluminate ions.
In the light of the above statements,choose the correct answer from the options given below.

In which of the following reactions, $MgO$ is not formed?