Aluminium is extracted from alumina (Al₂O₃) by electrolysis of a molten mixture of :

Al₂O₃ + HF + NaAlF₄
Al₂O₃ + CaF₂ + NaAlF₄
Al₂O₃ + Na₃AlF₆ + CaF₂
Al₂O₃ + KF + Na₃AlF₆

Solution

Fused alumina (Al₂O₃) is a bad conductor of electricity.Therefore,cryolite (Na₃AlF₆) and fluorspar (CaF₂) are added to purified alumina which not only make alumina a good conductor of electricity but also reduce the melting point of the mixture to around 1140 K.

Maximum pπ-pπ back bonding exists in

BCl₃
BF₃
BBr₃
BI₃

Solution

In BF₃, boron atom has vacant 2p_zA.O. and fluorine atom has electron pair in 2pA.O. so, maximum overlapping is possible between vacant 2p_z A.O. of boron and fully filled 2pA.O. of fluorine due to similar size of A.O’s.

Carborundum is obtained when silica is heated at high temperature with

carbon
carbon monoxide
carbon dioxide
calcium carbonate

Solution

Solution

R₃SiCl on hydrolysis forms only a dimer.
R₃SiOH + HOSiR₃ ⟶ R₃Si – O – SiR₃

Soldiers of Napolean army while at alps during freezing winter suffered a serious problem as regards to the tin buttons of their uniforms. White metallic tin buttons got converted to grey powder. This transformation is related to

a change in the partial pressure of oxygen in the air
a change in the crystalline structure of tin
an interaction with nitrogen of the air at very low temperatures
an interaction with water vapours contained in the humid air

Solution

When alumina is heated with carbon in the atmosphere of nitrogen then products formed are

Al + CO
Al + CO + N₂
Al + CO₂
AlN +CO

Solution

SiF₄ gets hydrolysed giving……..

SiO₂
Si(OH)₂F₂
H₂SiF₆
Si(OH)₄

Solution

It is hydrolysed with water to form a Si(OH)₄.

The type of glass used in making lenses and prisms is

Flint glass
Jena glass
Pyrex glass
Quartz glass

The form of BN which is as hard as diamond is

hexagonal form
Cubic form with ZnS structure
both of these
none of these

Solution

The cubic form of BN with ZnS structure is as hard as diamond.

Colour is imparted to glass by mixing

synthetic dyes
metal oxides
oxides of non-metals
coloured salts

Solution

Metal oxides or some salts are fused with glass to impart colour.

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