Ultra pure elemental silicon is prepared by the reduction of highly pure silicon tetrachloride(SiCl₄) or silicon chloroform(SiHCl₃) with dihydrogen
\({ SiCl }_{ 4 }+2{ H }_{ 2 }(g)\longrightarrow Si+4HCl\)
\({ SiHCl }_{ 3 }+{ H }_{ 2 }\longrightarrow Si+3HCl\)
It can also be prepared by the pyrolysis of SiH₄
\({ SiH }_{ 4 }\longrightarrow Si+{ 2H }_{ 2 }\)
Ultra pure elemental silicon is used as a semiconductor.

(a) Being acidic B₂O_3,Sio₂ and CO₂ react with alkalis to form salts
\(B_{ 2 }O_{ 3 }+2NaOH\rightarrow 2NaBO_{ 2 }+H_{ 2 }O\\ Boric\quad \quad \quad \quad \quad \quad sodium\quad metaborate\\ anhydride\)
\(SiO_{ 2 }+2NaOH\underrightarrow { D } Na_{ 2 }CO_{ 3 }+H_{ 2 }O\)
\(\\ Silica\quad \quad \quad \quad \quad \quad \quad \quad \quad Sodium\quad carbonate\\ CO_{ 2 }+2NaOH\rightarrow Na_{ 2 }CO_{ 3 }+H_{ 2 }O\\ Carbon\quad dioxide\quad \quad \quad sodium\quad carbonate\quad \quad \quad \quad \)
(b) Being amphotric, Al₂O₃ and PbO₂ react with both acids and bases.
\(Al_{ 2 }O_{ 3 }+3H_{ 2 }SO_{ 4 }\rightarrow Al_{ 2 }(SO)_{ 4 }+3H_{ 2 }O\)
\( Al_{ 2 }O_{ 3 }+2NaOH\overset { fuse }{ \rightarrow } \ 2NaAlO_{ 2 }+H_{ 2 }O\)
\(\\ Alumina\quad \quad \quad \quad \quad \quad \quad sodium\quad metaaluminate\\ 2PbO_{ 2 }+2H_{ 2 }SO_{ 4 }\rightarrow 2PbSO_{ 4 }+2H_{ 2 }O+O_{ 2 }\)
\(\\ PbO_{ 2 }+2NaOH\rightarrow Na_{ 2 }PbO_{ 3 }+H_{ 2 }O\\ Lead \ dioxide\quad \quad Sodium \ plumbate\)
(c) Being basic,Tl₂O₃ reacts with acid
\(Tl_{ 2 }O_{ 3 }+6HCl\rightarrow 2TICl_{ 3 }+3H_{ 2 }O\)

Silicon does not form \({ p\pi -p\pi }\) multiple bonds because of large size of silicon atom Hence, silicon does not form graphite-like structure as carbon does.

In this reaction, diborane is obtained 
aNaBH₄ +I₂\(\rightarrow\)B₂H₆ + 2NaI + H₂

Boric acid is sparingly soluble in cold water but fairly soluble in hot water. It acts as a weak monobasic acid. It is not a protonic acid but it acts as aLewis acid by accepting a hydroxide ion of water and releasing a proton into the solution.
H-OH + B(OH)₃\(\rightarrow\) [B(OH)₄]^- +H⁺

Among group 14 elements carbon is the most electronegative element

It is due to inert pair effect.

Inert pair effect:
The pair of electron in the valence shell does not take part in bond formation is called inert pair effect.

CO₂ is a greenhouse gas. About 75% of the solar energy reaching the earth is absorbed by the earth's surface. The rest of the heat radiates back to the atmosphere. But the heat radiated by the heated surface cannot pass freely into the space because excessive CO₂ in the atmosphere absorb more heat.
This results in increase in the average temperature of the atmosphere. This is known as global warming.

The catenation is maximum in carbon and decreases down the group. With increase in atomic size, electronegativity decreases and due to this, tendency to show catenation decreases, C-C bond enthalpy (348kJ mol^-1) is greater than Si-Si bond enthalpy (297kJmol^{- 1}). Therefore, C-C bond is stronger than Si-Si bond. That's why carbon has much higher tendency for catenation than silicon.

Hydrolysis of alkyltrichlorosilanes gives cross-linked silicons.

In BF_3' boron is sp² hybridized.
\(\therefore\) shape of BF₃= planar.
In [BH₄]^-, boron is sp³ hybridized, thus the shape is tetrahedral.