Select the correct option based on statements below:
Assertion (A): | Due to Frenkel defect, the density of the crystalline solid decreases. |
Reason (R): | In Frenkel defect cation and anion leave the crystal. |
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. |
The crystal with a metal deficiency defect is -
1. NaCl
2. FeO
3. ZnO
4. KCl
An element has a body-centered cubic (BCC) structure with a cell edge of 288 pm. The atomic radius is:
1. pm
2. pm
3. pm
4. pm
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. |
Select the correct option based on statements below:
Assertion (A): | Crystalline solids have sharp melting points. |
Reason (R): | Crystalline solids have definite enthalpies of fusions. |
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. |
If an element (at. Wt. = 50) crystallises in fcc lattice, with a = 0.50 nm, then the density of unit cell if it contains 0.25 % Schottky defect is -
(Use )
1. 2.0 g/cc
2. 2.66 g/cc
3. 3.06 g/cc
4. None of the above.
An element occurring in the bcc structure has unit cells. The total number of atoms of the element in these cells will be:
1.
2.
3.
4.
Select the correct option based on statements below:
Assertion (A): | The stability of a crystal is reflected by the magnitude of its melting point. |
Reason (R): | Greater the intermolecular forces of attraction, the higher will be the stability and melting point of the substance. |
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. |
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 %
Silver crystallizes in fcc lattice. If the edge length of the cell is 4.07 × 10−8 cm and density is 10.5 g cm−3, the atomic mass of silver is -
1. 120.31 g
2. 107.9 g
3. 207.60 g
4. 138.52 g