With the increase in atomic weights,the melting points of the alkali metals:

The oxide of $Cs$ is:

The $s$-block elements are characterised by their larger atomic sizes,lower ionisation enthalpies,invariable $+1$ oxidation state and solubilities of their oxosalts. In the light of these features,describe the nature of their oxides,halides and oxosalts.

The correct variation of the following properties of group $1$ elements $(M)$ ($Li$ to $Cs$) is:

The reaction of water with sodium and potassium is

When sodium metal is dissolved in liquid ammonia,a blue-coloured solution is formed. The blue colour is due to: