Which of the following is the strongest reducing agent?

Identify $X$ and $Y$, respectively in the following reactions:

What type of oxides do alkali metals form? Discuss some of the physical properties of these oxides.

The sequence of ionic mobility in aqueous solution is

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 .......

The solubility of alkali metal fluorides increases down the group. Select the correct explanation for the given statement.