Correct order of density is

What is the primary purpose of the Dow's process?

Hydroxide of which alkali metal is used in the manufacture of soft soap?

Which of the following carbonates of a metal has least thermal stability?

The atomic radii of alkali metals $(M)$ lie in the order $Li < Na < K < Rb$,but the radii of $M^{+}$ ions in aqueous solution lie in the reverse order $Li^{+} > Na^{+} > K^{+} > Rb^{+}$. What is the reason for this reverse order (on going from $Li$ to $Rb$)?

What is caused by an excess of $Na^+$ in the human body?