The electrical conductivity of semiconductors increases with a rise in temperature because:

1.	Electrons jump from the valence band to the conduction band.
2.	Electrons jump from the conduction band to the valence band.
3.	No electrons jump from the valence band to the conduction band.
4.	No electrons jump from the conduction band to the valence band.

The conductivity of germanium crystals increases on doping with galium because :

1. Occupation of lattice site of germanium by galium.

2. Occupation of lattice site of galium by germanium.

3. Of presence of extra electron in the lattice. 

4. None of the above.

In a compound, nitrogen atoms (N) make cubic close packed lattic and metal atoms (M) occupy one-third of the tetrahedral voids present. The formula of the compound formed by M and N is : 

1. M₂N₃

2. M₃N₂

3. MN

4. M₂N₄

Amorphous substance changes to crystalline form :

1. On  heating.

2. On pressure.

3. In light.

4. In UV source.

Mg in solid-state shows electronic conductivity due to the presence of-

1. Free electrons.

2. Positive holes.

3. No electrons.

4. None of the above

MgCl₂ in the molten state is-

1. p-type semiconductor

2. n-type semiconductor

3. Electrolytic conductors

4. Electronic conductors

Cubic close packing in three dimensions is

 1. Triangular voids

2. Pattern of spheres is repeated in every fourth layer

3. Coordination number =4

4. Pattern of sphere is repeated in alternate layers

Number of octahedral voids are present per unit cell in a cubic close packed structure :

1. 4

2. 8

3. 6

4. 2

Number of  tetrahedral voids voids are present per unit cell in a cubic close packed structure : 

1. 4

2. 8

3. 6

4. 2

Doping affects the property of semiconductors. It -

1. Increases the conductivity of semiconductors.

2. Decreases the conductivity of semiconductors.

3. No effect on conductivity of semiconductors.

4. None of the above.