Which one of the following does not react with water even under red hot condition? 

$$\begin{gathered} 2\mathrm{Na}+2{\mathrm{H}}_2\mathrm{O}⟶2\mathrm{NaOH}+{\mathrm{H}}_2\uparrow \\ 2\mathrm{K}+2{\mathrm{H}}_2\mathrm{O}⟶2\mathrm{KOH}+{\mathrm{H}}_2\uparrow \end{gathered}$$
All alkali metals decompose water with the evolution of hydrogen. 

$$\begin{gathered} \mathrm{Ca}+2{\mathrm{H}}_2\mathrm{O}⟶\mathrm{Ca}(\mathrm{OH}{)}_2+{\mathrm{H}}_2\uparrow \\ \mathrm{Sr}+2{\mathrm{H}}_2\mathrm{O}⟶\mathrm{Sr}(\mathrm{OH}{)}_2+{\mathrm{H}}_2\uparrow \\ \mathrm{Be}+2{\mathrm{H}}_2\mathrm{O}⟶\text{ No reaction } \end{gathered}$$
Ca, Sr, Ba and Ra decompose cold water readily with evolution of hydrogen. Mg decomposes boiling water but Be is not attacked by water even at high temperatures as its oxidation potential is lower than the other members.