Which of the following elements has the highest melting point?

The formula of borax is

When metal $X$ is treated with sodium hydroxide,a white precipitate $(A)$ is obtained,which is soluble in excess of $NaOH$ to give soluble complex $(B)$. Compound $(A)$ is soluble in dilute $HCl$ to form compound $(C)$. The compound $(A)$ when heated strongly gives $(D)$,which is used to extract metal. Identify $(X), (A), (B), (C)$ and $(D)$. Write suitable equations to support their identities.

Observe the following reactions (not balanced):
$BF_3 + LiAlH_4 \xrightarrow{(C_2H_5)_2O} X + LiF + AlF_3$
$X + NaH \longrightarrow Y$
The incorrect statement about $Y$ is:

Which of the following will not give a borax bead test?

Explain what happens when boric acid is heated.