Q.Explain why SiCl₄ undergoes hydrolysis readily. OR Why is aqueous solution of borax alkaline?

Unlike carbon, silicon (period 3) has energetically accessible empty $d$ orbitals, so water can attack the Si centre and hydrolyse the Si–Cl bonds.

$SiCl_4$ is readily hydrolysed by water because silicon, being in period 3, has vacant $3d$ orbitals of suitable energy. A water molecule's oxygen lone pair can attack the electrophilic Si centre, forming a five-coordinate transition state/intermediate (using one of these $d$ orbitals), after which a chloride ion leaves. Repeating this four times converts $SiCl_4$ into silicic acid / silica:

$SiCl_4 + 4H_2O \rightarrow Si(OH)_4 + 4HCl \quad (\text{or, on further dehydration, } SiO_2\cdot xH_2O)$

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