Why sodium is kept under kerosene?

Identify $\mathrm{A}$ (alkali metal) to $\mathrm{E}$.

Identify $\mathrm{A}$ to $\mathrm{D}$

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Identify $\mathrm{A}$ and  $\mathrm{E}$.

$$\begin{gathered} \mathrm{A}+\mathrm{NaOH}\stackrel{\mathrm{P},\mathrm{T}}{⟶}\mathrm{B}\stackrel{\mathrm{\Delta }}{⟶}\mathrm{C}\stackrel{{\mathrm{H}}^{+}}{⟶}\mathrm{D}\stackrel{{\mathrm{CaCl}}_2}{\to }\mathrm{E} \\ \mathrm{White} \mathrm{ppt}. \end{gathered}$$

Both $\mathrm{D}$ and $\mathrm{E}$ decolourize acidified ${\mathrm{KMnO}}_4$

Why does the following reaction:

$>\mathrm{C}-\mathrm{Cl}+\mathrm{MF}\to >\mathrm{C}-\mathrm{F}+\mathrm{MCl}$

Proceed better with $\mathrm{KF}$ than with $\mathrm{NaF}$?