21714.To get n–type doped semiconductor, the impurity to be added to silicon should have the following number of valence electrons?
1
2
3
5
21715.Three elements A, B and C crystalise into a cubic solid lattice. Atoms A occupy the corners, B occupies the cube centres and C occupies the edges. The formula of the compound is
ABC
ABC2
ABC3
ABC4
21716.Number of unit cells in 4 g of X (atomic mass = 40) which crystallize in bcc pattern is (NA= Avogadro number)
0.1 NA
2 × 0.1 NA
$\dfrac{0.1}{2}$NA
2 × NA
21717.The number of octahedral void(s) per atom present in a cubic close–packed structure is
2
4
1
3
21718.AB crystallizes in a body centred cubic lattice with edge length 'a' equal to 387 pm. The distance between two oppositively charged ions in the lattice is
300 pm
335 pm
250 pm
200 pm
21719.If 'a' stands for the edge length of the cubic systems: simple cubic, body centred cubic and face centred cubic, then the ratio of the radii of the spheres in these systems will be respectively:
$\dfrac{1}{2}a : \dfrac{\sqrt{3}}{4}a : \dfrac{1}{2\sqrt{2}}a$
$\dfrac{1}{2}a : \sqrt{3}a : \dfrac{1}{\sqrt{2}}a$
$\dfrac{1}{2}a : \dfrac{\sqrt{3}}{2}a : \dfrac{\sqrt{2}}{2}a$
$1a : \sqrt{3}a : \sqrt{2}a$
21721.Sodium chloride, NaCl, usually crystallizes in a face centred cubic lattice. How many ions are in contact with any single Na+ ion?
8
6
4
1
21722.The appearance of colour in solid alkali metal halides is generally due to
Schottky defect
Frenkel defect
Interstitial position
F–centres
21723.A compound formed by elements X and Y crystallizes in a cubic structure in which atoms X are at the corners of the cube and atoms Y are at the face–centers. The formula of the compound is
X3Y
XY
XY2
XY3
21724.The pyknometric density of sodium chloride crystal is 2.165 ×103 kg m–3 while its X–ray density is 2.178 × 103 kg m–3. The fraction of the unoccupied sites in sodium chloride crystal is
5.96
5.96 × 10–2
5.96 × 10–1
5.96 × 10–3
21725.Lithium metal crystallises in a body centred cubic crystal. If the length of the side of the unit cell of lithium is 351 pm, the atomic radius of the lithium will be:
300.5 pm
75.5 pm
151.8 pm
240.8 pm
21726.Total volume of atoms present in face–centred cubic unit cell of metal is (r is atomic radius)
$\dfrac{24}{3}\pi r^3$
$\dfrac{12}{3}\pi r^3$
$\dfrac{16}{3}\pi r^3$
$\dfrac{20}{3}\pi r^3$
21727.In a compound, atoms of element Y form ccp lattice and those of element X occupy 2/3 rd of tetrahedral voids. The formula of the compound will be
X3Y4
X4Y3
X2Y3
X2Y
21728.An ionic compound has a unit cell consisting of A ions at the corners of a cube and B ions on the centres of faces of the cube. The empirical formula of the compound would be
AB
A2B
AB3
A3B
21732.The edge length of a face centred cubic cell of an ionic substance is 508 pm. If the radius of the cation is 110 pm, the radius of the anion is
288 pm
144 pm
618 pm
398 pm