On heating Al at $800°\mathrm{C}$ in air, ${\mathrm{Al}}_2{\mathrm{O}}_3$ is formed. The reaction is:

1.  an endothermic reaction

2.  an exothermic reaction

3.  reduction of aluminium

4.  none of the above

Alumina on heating with carbon in nitrogen atmosphere gives:

1.  $\mathrm{Al}+\mathrm{CO}$

2.  $\mathrm{Al}+{\mathrm{CO}}_2$

3.  $\mathrm{AlN}+\mathrm{CO}$

4.  $\mathrm{Al}+\mathrm{CO}+{\mathrm{N}}_2$

Hoope's process is used in the refining of:

1.  Al

2.  Zn

3.  Ag

4.  Cu

The correct order of decreasing hardness of the following compounds is:

1.  Diamond > Borazon > Carborundum > Corundum

2.  Borazon > Diamond > Carborundum > Corundum

3.  Corundum > Carborundum > Borazon > Diamond

4.  none of the above

Aluminium becomes passive in nitric acid because it-

1. Is a noble metal

2. Forms a thin film of oxide

3. Has a positive reduction potential

4.  None of the above

Chemically thermite is -

1.  Fe and Al

2.  Ferric oxide and aluminium powder

3.  Barium peroxide and magnesium powder

4.  Cu and aluminium

${\mathrm{Al}}_2{\mathrm{O}}_3$ formation involves large quantity of heat evolution which makes its use in:

1.  deoxidizer

2.  confectionary

3.  indoor photography

4.  thermite welding

Al and Ga have the same covalent radii because of:

1. Greater shielding power of s-electrons of Ga atoms

2. Poor shielding power of s-electrons of Ga atoms

3. Poor shielding power of d-electrons of Ga atoms

4. Greater shielding power of d-electrons of Ga atoms

Which is used as mordant?

1.  ${\mathrm{AlCl}}_3$

2.  ${\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3$

3.  $\mathrm{Alum}$

4.  ${\mathrm{Al}}_2{\mathrm{O}}_3$

Hybridisation of boron in diborane is:

1.  $\mathrm{sp}$

2.  ${\mathrm{sp}}^2$

3.  ${\mathrm{sp}}^3$

4.  ${\mathrm{sp}}^3{\mathrm{d}}^2$