The phenomenon in which polar crystals on heating produce electricity is called:-

1. Pyro-electricity.
2. Piezo-electricity.
3. Ferro-electricity.
4. Ferri-electricity.

Which arrangement of electrons leads to anti-ferromagnetism?

1.  

2.  

3. Both (1) and (2)

4. None of the above.

A spinel is an important class of oxides consisting of two types of metal ions with the oxide ions arranged in ccp layers. The normal spinel has 1/8^th of the tetrahedral void occupied  by one type of metal and one half of the octahedral voids occupied by another type of metal ions. Such a spinel is formed by Zn²⁺, Al³⁺ and O^2- with Zn²⁺ in tetrahedral void. Give the simplest formula of the spinel.

1. ZnAl₂O₄

2. ZnAl₂O₃

3. ZnAlO

4. None of these

Among the following types of voids, which one is the largest void-

(1) Triangular system                             

(2) Tetragonal system

(3) Monoclinic system                             

(4) Octahedral

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

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.

MgCl₂ in the molten state is-

1. p-type semiconductor

2. n-type semiconductor

3. Electrolytic conductors

4. Electronic conductors

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.

Which of the following arrangements shows the schematic alignment of magnetic moments of antiferromagnetic substances? 

1. $\overline{)\uparrow }$ $\overline{)\uparrow }$ $\overline{)\uparrow }$ $\overline{)\uparrow }$ $\overline{)\uparrow }$ $\overline{)\uparrow }$

2. $\overline{)\downarrow }$ $\overline{)\downarrow }$ $\overline{)\downarrow }$ $\overline{)\downarrow }$ $\overline{)\downarrow }$ $\overline{)\downarrow }$

3. $\overline{)\uparrow }$ $\overline{)\uparrow }$ $\overline{)\downarrow }$ $\overline{)\uparrow }$ $\overline{)\uparrow }$ $\overline{)\downarrow }$

4. $\overline{)\uparrow }$ $\overline{)\downarrow }$ $\overline{)\uparrow }$ $\overline{)\downarrow }$ $\overline{)\uparrow }$ $\overline{)\downarrow }$

Graphite is a good conductor of electricity due to the presence of ......... .

(1) Lone pair of electrons.

(2) Free valence electrons.

(3) Cations.

(4) Anions.