Which metal burns in air at high temperature with the evolution of much heat?

Why is boric acid considered as a weak acid?

The crystalline form of borax has
$(A)$ tetranuclear $\left[B_4O_5(OH)_4\right]^{2-}$ unit
$(B)$ all boron atoms in the same plane
$(C)$ equal number of $sp^2$ and $sp^3$ hybridized boron atoms
$(D)$ one terminal hydroxide per boron atom

$AlCl_3$ in water at $pH < 7$ forms

In the following reaction,assign the correct description for the underlined atom in the product of complete hydrolysis at $R.T.$:
$\underline{I}Cl + H_2O \longrightarrow HIO + HCl$

Give the chemical reaction for the preparation of a borax bead.