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Answers
Answer:
1. Low temperature
2. Istrophic nature
3. Very low value of electrical conductivity in the molten state
4. Silicon exists as covalent crystals in the solid state.
5. 2N
6. 32%
7. 12
8. H.C.P. and C.C.P.
9. 8
10. NaCl
Explanation:
1. b At low temperature substance exists in solid state due to decrease in molecular motion which leads to strong cohesive forces i.e., forces which hold the constituent particles together.
2. b A crystalline solid is anisotropic in nature and not isotropic. The solid is anisotropic as this solid exhibits different physical properties such as the electrical resistance, and the refractive index in different directions. Both the isotropic and anisotropic properties are related to the amorphous solid and crystalline solid which can be clearly understood as -
Property - Isotropy and Anisotropy
Types of solid - Amorphous solid and Crystalline solid
Physical properties - Same value and Different values
3. a Very low value of electrical conductivity in the molten state
4. d Silicon exists as covalent crystals in the solid state.
5. b In a closed packed array of N spheres, the number of tetrahedral holes is 2N and the number of octahedral holes is N. For example, fcc unit cell has 4 atoms per unit cell. It has 4 octahedral and 8 tetrahedral voids.
6. a Percentage of free space in BCC unit cell is A) 32%. The ratio of volumes in unit cell occupied by atoms to the total unit cell volume is referred to as the packing fraction or packing density. For cubic structure centered around the body, Packing fraction = 68% of the unit cell is occupied by atoms.
7. a The hexagonal closest packed (hcp) has a coordination number of 12 and contains 6 atoms per unit cell. The face-centered cubic (fcc) has a coordination number of 12 and contains 4 atoms per unit cell. The body-centered cubic (bcc) has a coordination number of 8 and contains 2 atoms per unit cell.
8. H.C.P. and C.C.P. pairs of structures are tetrahedral and octahedral voids.
9. BCC stands for body centred cubic lattice. For BCC lattice co-ordination number is 8. - Thus potassium have co-ordination number 8 in the crystal structure.
10. NaCl