Dr. Vikas Yadav
November 3, 2021 at 3:18:27 AM
Directions: In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as:
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If both assertion and reason are false
1. Assertion: Quartz glass is crystalline solid and quartz is an amorphous solid.
Reason: Quartz glass has long range order.
2. Assertion: Graphite is a good conductor of electricity however diamond belongs to the category of insulators.
Reason: Graphite is soft in nature on the other hand diamond is very hard and brittle.
3. Assertion: In crystalline solids, the value of resistance is different in different directions.
Reason: Crystalline solids are isotropic in nature.
4. Assertion: Glass panes fixed to windows or panes of old buildings are found to be slightly thicker at the bottom.
Reason: Amorphous solids have a tendency to flow.
5. Assertion: Face-centred cubic cell has four atoms per unit cell.
Reason: In fcc unit, there are eight atoms at the corner and six atoms at face centers.
6. Assertion: CsCl has body centred cubic arrangement.
Reason: CsCl has one Cs+ ion and eight Cl– ions in its unit cell.
7. Assertion: In crystal lattice, the size of the tetrahedral hole is large than an octahedral hole.
Reason: The cations occupy more space than anions in crystal packing.
8. Assertion: On heating ferromagnetic or ferrimagnetic substances, they become paramagnetic.
Reason: The electrons change their spin on heating.
9. Assertion: The total number of atoms present in a simple cubic unit cell is one.
Reason: Simple cubic unit cell has atoms at its corners, each of which is shared between eight adjacent unit cells.
10. Assertion: The packing efficiency is maximum for the fcc structure.
Reason: The coordination number is 12 in fcc structures.
Answers -
1. (d)
Explanation - Quartz glass is an amorphous solid because it is formed by fusing the crystal which is then cooled rapidly. Whereas, quartz, like all other minerals, is a crystalline solid with the molecular formula SiO2. Quartz glass has no long range order because the components in its structure are not arranged in regular arrays whereas crystalline solids have regular long range order because the components in its structure are held together by uniform inter-molecular forces and they have a certain pattern of atoms that is repeated over and over in three dimension. Thus, both assertion and reason are false.
2. (b)
Explanation - Diamond is bad conductor of electricity because valence electrons of carbon are involved in bonding. In graphite, however, three out of four valence electrons are involved in bonding and the fourth electron remain free between adjacent layers which makes it a good conductor. Graphite is soft because parallel layers are held together by weak Van der Waal’s force. However, diamond is hard due to compact three dimensional network of bonding. Thus, both assertion and reason are true, but reason is not the correct explanation of assertion.
3. (c)
Explanation - Crystalline solids are anisotropic in nature i.e., some of their physical properties such as electrical resistance or refractive index show different values along different directions due to different arrangement of particles in different directions. Thus, assertion is correct but reason is not correct.
4. (a)
Explanation - Amorphous Solids have a tendency to flow, though very slowly. Glass is sometimes called a super-cooled liquid because it does not form a crystalline structure, but instead forms an amorphous solid that allows molecules in the material to continue to move. This is the reason that the glass panes fixed to windows or panes of old buildings are found to be slightly thicker at the bottom than at the top because glass is pseudo solid or super-cooled liquid. Thus, both assertion and reason are true and reason is the correct explanation of assertion.
5. (a)
Explanation - The face-centred cubic structure has atoms located at each of the corners and the centres of all the cubic faces. Each of the corner atoms is the corner of another cube so the corner atoms are shared among eight-unit cells. Thus, both assertion and reason are true and reason is the correct explanation of assertion.
6. (c)
Explanation - CsCl has body centred cubic arrangement but it has one Cs+ ion and one Cl– ion in its unit cell. Thus, assertion is true but reason is false.
7. (d)
Explanation - In a crystal lattice, Tetrahedral holes are smaller in size than an octahedral holes. Cations usually occupy less space than anions. Thus, both assertion and reason are false.
8. (a)
Explanation - All magnetically ordered solids (ferromagnetic, ferrimagnetic and anti frerromagnetic solids) transform to the paramagnetic state at high temperature due to the randomisation of spins i.e., electrons change their spin on heating. Thus, both assertion and reason are true and reason is the correct explanation of assertion.
9. (a)
Explanation - In a simple cubic unit cell, atoms are present at each corners and each of it is shared between eight adjacent unit cells. Therefore, the total number of atoms present in a simple unit cell is 8 × (1/8) = 1. Thus, both assertion and reason are true and reason is the correct explanation of assertion.
10. (b)
Explanation - The coordination number is 12 in fcc structures and In fcc unit cell, CCP arrangement is present with packing efficiency of 74 % which is maximum. Thus, both assertion and reason are true, but reason is not the correct explanation of assertion.