In which of the following crystals are alternate tetrahedral voids occupied:

1. NaCl

2. ZnS

3. CaF₂

4. Na₂O

The value of

${\int }_0^{\mathrm{\pi }/4}({\tan }^{\mathrm{n}-2}<mspace\; width="1em"></mspace>\mathrm{x}+{\tan }^{\mathrm{n}}<mspace\; width="1em"></mspace>\mathrm{x})\mathrm{d}(\mathrm{x}-[\mathrm{x}]-[\mathrm{x}{]}^2-\left[\mathrm{x}{]}^3\right)$

where [x] is greatest integer function, is

1. 1/n

2. 1/n + 2

3. 1/n + 1

4. 1/n - 1

In a compound, atoms of element Y form ccp lattice, and those of element X occupy 2/3^rd of tetrahedral voids. The formula of the compound will be :-
1. X₃Y₄
2. X₄Y₃ 
3. X₂Y₃
4. X₂Y

The anions (A) form hexagonal closest packing and atoms (C) occupy only 2/3 of octahedral voids in it. The general formula of the compound is-
1. CA
2. CA₂
3. C₂A₃
4. C₃A₂

A solid has a bcc structure. If the distance of closest approach between the two atoms is 1.73 Å, then the edge length of the cell is:

1. 200 pm

2. \(\frac{\sqrt{3}}{\sqrt{2}}\) pm

3. 142.2 pm

4. \(\sqrt{2 }\)pm

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

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

The unit cell dimensions of a cubic lattice (edges a, b, c and the angles between them, α, β, γ) are : 

1. a = b = c, $\mathrm{\alpha <mspace\; width="1em"></mspace>}=\hspace{0.17em}\mathrm{\beta <mspace\; width="1em"></mspace>}=\hspace{0.17em}\mathrm{\gamma <mspace\; width="1em"></mspace>}=\hspace{0.17em}90°$

2. a = b $\ne \hspace{0.17em}$c, $\mathrm{\alpha <mspace\; width="1em"></mspace>}=\hspace{0.17em}\mathrm{\beta <mspace\; width="1em"></mspace>}=\hspace{0.17em}\mathrm{\gamma <mspace\; width="1em"></mspace>}=\hspace{0.17em}90°$

3. a = b = c, $\mathrm{\alpha <mspace\; width="1em"></mspace>}=\hspace{0.17em}\mathrm{\gamma <mspace\; width="1em"></mspace>}=\hspace{0.17em}90°,$ $\mathrm{\beta <mspace\; width="1em"></mspace>}\ne \hspace{0.17em}90°$

4. a $\ne \hspace{0.17em}$b $\ne \hspace{0.17em}$c, $\mathrm{\alpha <mspace\; width="1em"></mspace>}=\hspace{0.17em}\mathrm{\beta <mspace\; width="1em"></mspace>}=\hspace{0.17em}90°,$ $\mathrm{\gamma <mspace\; width="1em"></mspace>}\ne \hspace{0.17em}90°$

The incorrect statement among the following is -