The metal-pair that can produce nascent hydrogen in alkaline medium is

Select the correct statement from the following.

The strongest reducing agent among the alkali metals is

In Solvay process,$NH_3$ is recovered when the solution containing $NH_4Cl$ is treated with compound ' $X$ '. What is ' $X$ ' ?

Which of the following metallic hydroxides does not dissolve in a solution of sodium hydroxide?

By which method can the concentration of alkali metals be determined?