Select the correct option based on statements below:

Assertion (A):	Ferromagnetic solids become paramagnetic upon heating.
Reason (R):	Unpaired electrons starts pairing upon heating.

 

1.	Both (A) and (R) are true and (R) is the correct explanation of (A).
2.	Both (A) and (R) are true but (R) is not the correct explanation of (A).
3.	(A) is true but (R) is false.
4.	Both (A) and (R) are false.

An element has a body-centered cubic (BCC) structure with a cell edge of 288 pm. The atomic radius is:

1. $\frac{\sqrt{2}}{4}\times 288$ pm

2. $\frac{4}{\sqrt{3}}\times 288$ pm

3. $\frac{4}{\sqrt{2}}\times 288$ pm

4. $\frac{\sqrt{3}}{4}\times 288$ pm

The crystal with a metal deficiency defect is - 

1. NaCl 

2. FeO

3. ZnO 

4. KCl

The formula of nickel oxide with metal deficiency defect in its crystal is $N{i}_{0.98}O$. The crystal contains ${\mathrm{Ni}}^{2+}<mspace\; width="1em"></mspace>\mathrm{and}<mspace\; width="1em"></mspace>{\mathrm{Ni}}^{3+}$ ions. The fraction of nickel existing as $N{i}^{2+}$ ions in the crystal is-

1. 0.96

2. 0.04

3. 0.50

4. 0.31

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

If NaCl is doped with ${10}^{-5}$ mol% of $SrC{l}_2$, the number of cation vacancies will be - 

1. $6.02\times {10}^{16}$                 

2. $6.02\times {10}^{18}$

3. $6.02\times {10}^{20}$                 

 4. 2$\times 6.02\times {10}^{23}$

Select the correct option based on statements below:

The packing efficiency of the face-centered cubic unit cell is:
(assuming that the atoms are touching each other)

1. 52.40 %

2. 68.04 %

3. 74 %

4. 79.06 %

Copper crystallizes into an fcc lattice with an edge length of 3.61 × 10⁻⁸ cm. The density of copper crystal will be - 

1. 7.46 g cm^-3

2. 9.67 g cm^-3

3. 8.96 g cm^-3

4. 5.63 g cm^-3

A compound is formed by two elements M and N. The element N forms ccp and atoms of M occupy 1/3rd of tetrahedral voids. The formula of the compound would be -

1. MN

2. M₃N₄

3. M₂N₃

4. M₃N₂