Schottky defect is a type of point defect in crystal lattice named after walter $H$ scottky. In non$-$iodic crystals, it means a lattice vacany defect. In ionic$-$crystals, the defect forms when oppositely charged ions leave their lattice sites, creating vacancies.
Eg$. \text{AgBr, NaCl}.$
$\Rightarrow$ Schottky defect abserved in $\text{NaCl}$ crystal.
The empty space in $\text{hcp}$ and $\text{ccp}$ is about:
✓
$26\%$
B
$30\%$
C
$35\%$
D
$40\%$
Answer
Correct option: A.
$26\%$
The space occupied by spheres of equal size in three dimensions in both $\text{hcp}$ and $\text{ccp}$ arrangements is $74\%.$
The vacant space is $100 − 74 = 26\%.$
The structure of graphite consists of many flat layers of hexagons. The layers are called graphene sheets. Each carbon atom in the layer is joined by strong covalent bonds to only three other carbon atoms. Compare this with the structure of diamond. Each graphene sheet is itself a giant molecule.
Which of the following is true about the value of refractive index of quartz glass?
✓
Same in all directions.
B
Different in different directions.
C
Cannot be measured.
D
Always zero.
Answer
Correct option: A.
Same in all directions.
Since quartz glass is an amorphous solid having short range order of constitutents. Hence, value of refractive index is same in all directions, can be measured and not be equal to zero always.
Ice has hydrogen bonding and covalent bond, and intermolecular hydrogen bonds are weaker than Covalent bonds.
$H-O$ are covalent bonds$. H-O$ are intermolecular hydrogen bonding also with other neighbouring atoms.