Molten sodium is used in nuclear reactors to

Which of the following is most soluble in water?

Fill in the blanks:
$(1)$ Lithium on reaction with nitrogen present in air is denoted by .....
$(2)$ Potassium gives ...... colour in oxidizing flame.
$(3)$ ....... and ........ metals are used in photoelectric cells.
$(4)$ When alkali metal dissolves in ammonia,it produces a blue-coloured solution. This colour is due to .......

In the presence of which of the following does magnesium continue to burn?

The stability order of oxide,peroxide,and superoxide of alkali metals is:

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