Answer:
(i) Silicones are organosilicon
polymers containing
Si?O?Si linkages. They contain
repeated \[\left[ -O-\underset{\underset{\text{R}}{\mathop{\text{
}\!\!|\!\!\text{ }}}\,}{\overset{\overset{\text{R}}{\mathop{\text{
}\!\!|\!\!\text{ }}}\,}{\mathop{Si}}}\,- \right]\]
units. Silicones are non-toxic,
stable towards heat and are hydrophobic (water repellent) in nature.
Uses:
(a) Silicones are used in making
waterproof cloth, paper, wool, wood, etc., by exposing them to silicone vapour.
(b) Silicone oils are used as
lubricants at high as well as low temperatures.
(c) These are used as insulating
materials for electric motors and other electrical appliances.
(d) Silicone rubbers are useful
as they retain their elasticity over a range of temperatures.
(e) These are mixed with paints
and enamels to make them resistant to the effect of high temperature, sunlight
and damp.
(ii) Boron forms a number of
hydrides. These are called boranes. Boranes can be grouped into two series :
(a) \[{{B}_{n}}{{H}_{n+4}}:{{B}_{2}}{{H}_{6}},{{B}_{5}}{{H}_{9}},{{B}_{10}}{{H}_{14}},etc.\]
(b) \[{{B}_{n}}{{H}_{n+6}}:{{B}_{4}}{{H}_{10}},{{B}_{5}}{{H}_{11}},{{B}_{9}}{{H}_{15}},etc.\]
The simplest boron hydride, \[B{{H}_{3}}\]
is unknown. The most important hydride is diborane,
\[{{B}_{2}}{{H}_{6}}\].
It is prepared by the action of \[LiAl{{H}_{4}}\]
on boron trichloride in presence of ether.
\[4BC{{l}_{3}}+3LiAl{{H}_{4}}\xrightarrow{{}}2{{B}_{2}}{{H}_{6}}+3LiCl+3AlC{{l}_{3}}\]
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