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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 551. |
Why does the elctrical conductivity fo semiconductors increase with rise in temperature ? ltbr |
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Answer» Correct Answer - In semiconductors, the gap between conduction band and valence band is small. Therefore, on increasing temperature, electrons can easily jump from valence band to conduction band. As a result, electical conductivity increases. |
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| 552. |
why does white Zn0(s) becomes yellow upon heating ? |
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Answer» on heating ZnO loses oxygen as follows `ZnOoverset("heat")to Zn^(2+)+(1)/(2)O_(2)+2e^(-)` `Zn^(2+)` ions and electrons move to interstitial sites and F - centress are formed which imparat yellow colour to ZnO(S) . |
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| 553. |
In the fluorite structure if the radius ratio is `(sqrt((3)/(2))-1)`, how many ions does each cation touch ?A. 4 anionsB. 12 cationsC. 8 anionsD. No cations |
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Answer» Correct Answer - 2 In fluorite structure, cations from the lattice & anions occupy each of tetrahedral voids. |
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| 554. |
Tugsten has a density of ` 19.35 " g cm"^(-3)` and the length of the side of the unit cell of 316 pm. The unit cell in the most important crystalline from of tungsten is the body centred cubic unit cell. How many atoms of the element does 50g of the element contain ? |
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Answer» Correct Answer - 2,i.e, BCC |
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| 555. |
In which of the following crystals alternative tethedra void are occupies ?A. NaClB. ZnSC. `CaF_(2)`D. `Na_(2)O` |
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Answer» Correct Answer - A In ZnS structure sulphide ions occupy all fccd lattice points while `Zn^(2+)` ions are present in alternate tetrahedral voids. Hence (B) is correct option. |
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| 556. |
As element cystallises in BCC structure. The edge length of its unit cell is 288 pm. It the density of the crystals is ` 7.2 g cm^(-3)` , what is the atomic mass of the element ? (b) How many atoms of the element are presnet in 100g ? |
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Answer» Correct Answer - `107. 9 " mol"^(-1)` |
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| 557. |
A salt AB cystallises in the CsCl structure. The anions at the corners and the cation in the centre. Hence, radius ratio `r_(+)//r_(-)`A. 0.225B. 0.441C. 0.625D. 0.732 |
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Answer» Correct Answer - 4 for bcc `r_(c)//r_(a)=0.732` or above |
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| 558. |
Which of the following will produce p-type semiconductor?A. Silicon doped with phosphonusB. Germanium doped with arsenicC. Gallium doped with anenicD. Germanium doped with gallium |
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Answer» Correct Answer - 4 Germanium is group 14 element while gallium is group 13 element Hence, ahole will be created, i.e., it will bep-type semiconductor. |
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| 559. |
Distinguish between intrinsic and extrinsic semi-conductors on the basis of energy band diagram.A. Schottky defectB. ChemicalsC. Frenkel defectD. Both 1 and 2 |
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Answer» Correct Answer - 2 extrinisic semiconductors are formed by addition of impuirty to intrinsic semiconductors. |
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| 560. |
A pure crystallic substance , on being heated gradually first a hurbit looking liquid and then the furbidly completely disppears .This behaviour is the characteristic of substances formingA. Isomeric crystalsB. liquid crystalsC. isomorphous crystalD. Allotropic crystals |
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Answer» Correct Answer - b It is a characteristic of liquid crystal. |
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| 561. |
The number of carbon atoms per unit cell of diamond unit cell isA. 1B. 4C. 8D. 6 |
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Answer» Correct Answer - C In the diamond cubic unit cell, there are eight corner atoms, six face centered atoms and four more atoms inside the structure. `therefore` Number of atoms present in a diamond cubic unit cell =1+3+4=8 atoms. |
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| 562. |
A pure crystallic substance , on being heated gradually first a hurbit looking liquid and then the furbidly completely disppears .This behaviour is the characteristic of substances formingA. Isomeric crystalsB. Liquid crystalsC. Isomorphous crystalsD. Allotropic crystals |
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Answer» Correct Answer - B It is a characteristic of liquid crystal. |
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| 563. |
Calculate the value of Avogadro number from the internuclear distance of adjacent ions in `NaCl, 0.282 nm` and the density of solid `NaCl` is `2.17xx10^(3)kg//m^(3)` . A unit cell contains `4 NaCl` formula units. |
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Answer» Correct Answer - `6.01xx10^(23);` |
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| 564. |
The electrical conductivity of semiconductors ……. With increase of temperature. |
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Answer» Correct Answer - intrinsic |
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| 565. |
A hexagonal close-packed lattic can be represented by figures (a) and (b) below. If `c=asqrt((8)/(3))=1.633a` , there is an atom at each corner of the unit cell and another atom which can be located by moving one-third the distance along the diagonal of the rhombus base, starting at the lower left hand corner and moving perpendicularly upward by c/2 . Mg crystallizes in this lattice and has a density of `1.74 g cm^(-3)`. What is the volume of unit cell?A. 46B. 20C. 180D. 90 |
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Answer» Correct Answer - A `Z_(eff)`=8 (corners)`xx(1)/(8)` (per corner share)+1 (in the body)=2 atoms/unit cell. Aw of Mg=24.3g Mass=(2 atoms) `((24.3g)/(6.02xx10^(23)"atoms"))=8.07xx10^(-23)g` volume= `("Mass")/("Density")=((8.07xx10^(-23)g)/(1.74gcm^(-3)))xx(10^(8)overset(@)A)^(3)=46.4overset(@)A^(3)` |
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| 566. |
The electrical conductivity of semiconductors ……. With increase of temperature.A. Increases with temperatureB. Decreases with temperatureC. Remains constant on heatingD. All the above |
| Answer» Correct Answer - 1 | |
| 567. |
If arsenic is added as impurity to silicon, the type of semiconductor obtained is called ….. |
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Answer» Correct Answer - p -type |
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| 568. |
Which type of semiconductor is obtained by mixing arsenic with silicon?A. n-typeB. p-typeC. InternalD. Both 1 and 2 |
| Answer» Correct Answer - 1 | |
| 569. |
Consider an ionic solid MX with NaCl structure. Construct a new structure (Z) whose unit cell is constructed from the unit cell of MX following the sequential instructions given below. Neglect the charge balance. (i) Remove all the anions (X) except the central one (ii) Replace all the face centered cations (M) by anions (X) (iii) Remove all the corner cations (M) (iv) Replace the central anion (X) with cation (M) The value of `(("Number of anions")/("number of cations"))` in Z is _________ |
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Answer» Correct Answer - 3 `X^(o+)rArrO.V`. `M^(+)rArrF C C` `M^(+) X^(-)` (i) 4 1 (ii) 4-3 3+1 (iii) 4-3-1 3+1 (iv) 1 3 `Z=(3)/(1)=3` |
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| 570. |
Match the entries listed in Column I with appropriate entries listed in Column II |
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Answer» Correct Answer - `Ararrq;Brarrp;Crarrs;Drarrs` `Ararrq,Brarrp,Crarrs,Drarr r` (A) Intercepts of the shaded plane =a,b,c. Miller indices =111. (B) Intercepts of the shaded plane =a,-b,c or -a,b,-c. miller indices=111 or 111. (C) Intercepts of the shaded plane =a,-b,-c or -a,b,c. Miller indices =111 or 111 (D) Intercepts of the shaded plane =a,b,-c or -a,-b,c Miller indices =111 or 111. |
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| 571. |
Match the entries listed in Column I with appropriate entries listed in Column II |
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Answer» Correct Answer - `Ararrr;Brarrp;Crarrq;Drarrs` `Ararrr,Brarrp,Crarrq,Drarrs` (A) Atom A/unit cell `=8xx(1)/(8)=1` Atoms B/unit cell `=6xx(1)/(2)=3`. Formula `=AB_(3)` (B) Atoms A/unit cell `=8xx(1)/(8)+6xx(1)/(2)=4` Atoms B/unit cell `=12xx(1)/(4)=3`. Formula `=A_(4)B_(3)` (C) Suppose anions B=n. Octahedral voids =n, Tetrahedral voids=2n Cation A=n(in octahedral voids)+n (in tetrahedral voids)`=2n therefore A:B=2n:n=2:1` Formula =`A_(2)B` (D) Suppose cations `A=n` Tetrahedral voids =2n ,brgt Anions B=2n `therefore A:B=n:2n=1:2` Formula `=AB_(2)`. |
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| 572. |
Which is true ? If radius ratio `r^(+)//r^(-)`A. is `0.732 "to" 0.414` co-ordination number is 6 and is octahedralB. is above `0.732` , co-ordination number is 8 and is cubicC. is `0.225 "to" 0.155` co-ordination number is 3 and is triangularD. is `0.732 " to " 0.878`, co-ordination number is 8 and is cubic |
| Answer» Correct Answer - A::B::C | |
| 573. |
In the figure given below, four parallelograms are shown. How many parallelograms are a unit cells? |
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Answer» Correct Answer - 2 Statements `(a), (b)`, and `(c)` are correct. So total score `= 1 + 2 + 3 = 6` Statement `(a,b)` are factual. Statement `(c) : (r_(o+))/(r_(ɵ)) = (0.35)/(0.95) = 0.368` The radius ratio lies in the range of `0.225 - 0.414`, which corresponds to `TV` and the `CN` of `TV = 4`. |
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| 574. |
Glasses and plastics areA. amorphous solidsB. super cooled liquidsC. isotropicD. ferromagnetic |
| Answer» Correct Answer - A::B | |
| 575. |
Which of the following statements are correct ?A. In a body- centred cubic unit cell, the C.N is 12B. The C.N. of each type of ion in CsCl is 8C. A unit cell of an ionic crystal shares some of its ions with neighbouring unit cellsD. `r_(Na^(+))=95"pm", r_(Cl^(-))=181"pm"` , then the edge length of the unit cell of NaCl is 552pm |
| Answer» Correct Answer - B::C::D | |
| 576. |
The following figure shows the unit cell of a compound, i.e., a mixed oxide of yttrium, bariym, and copper. The formula of mixed oxide is `Y_(a)Ba_(b)Cu_(c)O_(d)`. Find the value of `(a + b+ c + d)`. |
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Answer» Correct Answer - 13 Singal unit cell consists of thrre cubes. ltbRgt Number of `Ba^(2+)` ions `= 2` per lunit cell Number of `Y^(4+)` ions `= 1` per unit cell Number of `Cu^(2+)` ions `= 8` in each at corners) `= 8 xx 3` (in three cubs) `xx 1/8` (per corner share) `= 3//"unit cell"` Number of `O^(2-)` ions `= 10` (at edge centre of cube `1`) `+ 8` (at eedge centre of cube `2`) `+ 10` (at edge centre of cube `3`) `= 28` (edge centre) `xx 1/4` (per edge centre share) `= 7//"unit cell"` Formula: `Y_((a))^(4+)Ba_((b)^(2+))Cu_((c)^(2+))O_((d)^(2-))` `rArr Y_(1^(4+))Ba_(2^(2+))Cu_(3^(2+))O_(7^(2-))` `[{:("Total +ve charge (14)"),("is equal to total" -ve),("charge" (14)):}]` `:. a + b + c + d = 1 + 2 + 3 + 7 = 13` |
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| 577. |
CsCl structure is interchanged into NaCl structure. This can be done becauseA. Temperature is increasedB. Pressure is decreasedC. Temperature is decreasedD. Pressure is increased |
| Answer» Correct Answer - A::B | |
| 578. |
In `CsCl` the number of formula units per unit cell isA. `2`B. `4`C. `6`D. `12` |
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Answer» Correct Answer - 1 Caesium chloride consists of positive ions `(Cs^(+))` ion and one negative ions `(CI^(-))` of about equal size arranged in a cubic array.There are chloride ions at each cornor of the cube and a caesium ion at the centre.Alternative the unit cell may be taken to have caesium ions at the corners of a cube and a chloride ion at the centre. In either case the unit cell contains one `Cs^(+)` ion and one `CI^(-)` ion:`(1)/(8)Cl^(-)` ion (or `(1)/(8)Sc^(+)`ion) at each of eight corners plus `Cs^(+)` ion (or more `CI^(-)` ion ) at each of the unit cell. |
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| 579. |
Which of the following is polymorphic?A. Caesium chlorideB. Sodium chlorideC. Zinc sulphideD. Both (1) and (2) |
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Answer» Correct Answer - 3 A solid substance that can occur in more than one crystal structure is said to be polymorphic.Zince sulphide `(ZnS)` crystallizes in either of two structures .The Zinc sulphide minearl having cubic structure is called zinc blende (or sphalerite). Zinc sulphide also exists as hexagonal crystals.The mineral is called wurtzite. |
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| 580. |
The following figure shows the unit cell of a compound, i.e., a mixed oxide of yttrium, barium , and copper. The formula of mixed oxide is `Y_(a)Ba_(b)Cu_(c)O_(d)` . Find the value of `(c+d)-(a-b)`. |
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Answer» Correct Answer - 7 Single unit cell consists of three cubes. Number of `Ba^(2+)` ions =2 per unit cell Number of `Y^(4+)` ion=1 per unit cell Number of `Cu^(2+)` ions=8 in each cube at corners) `=8xx3` (in three cubes) `xx(1)/(8)` (per corner share)=3/unit cell. Number of `O^(2-)` ions=10(at edge center of cube 1)+8 (at edge center of cube2) +10 (at edge center of cube3)=28 (edge center) `xx(1)/(4)` (per edge center share)=7//unit cell Formula `^(4+)Ba^(2+)Cu^(2+)O^(2-)` `Y_(1)^(4+)Ba_(2)^(2+)Cu_(3)^(2+)O_(7)^(2-)` [Total +ve charge (14) is equal to total -ve charge (14)] `therefore (c+d)-(a+b)=7+3-(1+2)=7` |
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| 581. |
At room temperature a substance exists in the solid state only whenA. intermolecular forces balance thermal energyB. intermolecular forces are stronger than thermal energyC. thermal enegry dominates over intermoleacular forcesD. there are oppositely charged ions present. |
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Answer» Correct Answer - B A substance exists as solid when intermolecular forces are stronger than thermal energy. |
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| 582. |
The `ZnS` structure can be obtained from theA. rock salt structure by replacing the `Na^(+)` and `Cl^(-)` ions of each basis with one `Zn` atoms and one `S` atom respectivelyB. fullferene structure by replacing the two `C` atoms of each basis with one `Zn` atoms and one `S` atom.C. graphite structure by replacing two `C` atoms of each basis with one `Zn` atom and one `S` atom respectively.D. diamond structure by replacing the two `C` atoms of each basis with one `Zn` atom and one `S` atom respectively. |
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Answer» Correct Answer - 4 Diamond structure is similar to that of sphalerite ( or Zinc blende) .In a unit cell of zinc blende ,sulphide ions are at the corners and at the centre of each faces of the unit cell.The position of the Zinc ions can be described if we imagine the unit cell divided into eight cubic parts ,or subcubes,Zinc ions are at the centres of alterante subcubes,the number of `S^(2-)` ions per unit cell is four `(8 "corner ions" xx(1)/(8)+6"face ions")xx(1)/(2)` and the number of `Zn^(2+)` ions is four (All the completely within the unit cell). Thus ,there are equal number of `Zn^(2+)` and `S^(2-)` ions as expected by the formula `ZnS`.Diamond structure is obtained if each `Zn^(2+)` ion and each `S^(2-)` ion is replaced by `C` atoms. |
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| 583. |
Which of the following statements is not true about NaCl struture ?A. MgB. ZincC. CopperD. Lithium |
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Answer» Correct Answer - D Lithium is body centred cubic. |
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| 584. |
If all three iterfacial angeles defining the unit cell, are equal in magniture, the crystal cannot be:A. rhombohedralB. cubicC. hexagonalD. tetragonal |
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Answer» Correct Answer - C |
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| 585. |
Which of the following statements is not true about NaCl structure?A. `Cl^(-)` ions are in fcc arrangementB. `Na^(+)` ions has coordination number 4C. `Cl^(-)` ions has coordination number 6D. Each cell contains 4 NaCl molecules |
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Answer» Correct Answer - B In NaCl, `Na^(+)` present in octahedral void hence C . N . = 8 |
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| 586. |
An ionic compound is expected to have tetrahedral structure if `r_(x)//r_(-)` lies in the range ofA. 0.155 to 0.225B. 0.732 to 0.414C. 0.414 to 0.732D. 0.225 to 0.414 |
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Answer» Correct Answer - D For tetrahedral void `r_(+)/r_(-)` range will be `0.225 lt (r^(+))/(r^(-)) 0.414` |
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| 587. |
For tetrahedral coordination number, the radius ratio `(r_(c^(+)))/(r_(a^(-)))` is :A. 0.732-1.000B. 0.414-0.732C. 0.225-0.414D. 0.155-0.225 |
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Answer» Correct Answer - C For tetrahedral arrangement co-ordination number is 4 and radius ratio `(r_(+)//r_(-))` is 0.225-0.414. |
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| 588. |
For tetrahedral coordination number, the radius ratio `(r_(c^(+)))/(r_(a^(-)))` is :A. 0 to 0.155B. `0.115-0.225`C. `0.225-0.414`D. `0.414-0.732` |
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Answer» Correct Answer - C For tetrahedral shape (C.N.= 4 ), the limiting radius ratio is `0.225-0.414` . |
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| 589. |
What are piezo-electric crystals ? |
| Answer» These are the crystals which upon applying mechanical stress produce electricity. | |
| 590. |
What are photo- voltaic compounds ? |
| Answer» Compounds which generate current when exposed to light are called photovoltaic compounds. | |
| 591. |
What is the C.N. of octahedral void ? |
| Answer» The C.N. of octahedral void is six. | |
| 592. |
Calculate the number of unit cells in 8.1 g of aluminium if it crystalliz3es in aface cented cubic (f.c.c) structure. (Atomic mass of Al= 27 `g mol^(-1) `) |
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Answer» 1 mole of Al ` = 27 g = 6.02 xx 10^(23) ` atoms No, of Al atoms present in 8.1 g of Al ` = ( 6.02 xx 10^(23))/ 27 xx 8.1 = 1.806 xx 10^(23)` As face- centred cubic unit cell contains 4 atoms, therefore, Number of unit cells present =` (1.806 xx 10^(23))/4 = 4.515 xx 10^(22)` |
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| 593. |
A solid AB has rock salt structure. How many atoms of A and B are present in the unit cell ? |
| Answer» It has four atoms of A as well as of B per unit cell. | |
| 594. |
Arrange simple cubic, body centred cubic and face cented cubic lattic in increasing order of the fraction of the occupied space. |
| Answer» Simple cubic lt Body centred cubic lt Face centred cubic. | |
| 595. |
Compute the percentage void space per unit volume of unit cell in zinc-fluoride structure .A. `25.07 %`B. `74.93 %`C. `52%`D. `48%` |
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Answer» Correct Answer - A Since anions occupy fcc positions and half of the tetrahedral holes are occupied by cations. Since there are four anions and 8 tetrahedral holes per unit cell, the fraction of volume occupied by spheres/unit volume of the unit cell is Q for tetrahedral holes, `=0.225=(1+(0.255)^(3))=0.7493` `therefore` void volume=1-0.7493 =0.2507 / unit volume of unit cell % void space=25.07% |
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| 596. |
ccp as same as withA. bccB. fccC. hcpD. none of these |
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Answer» Correct Answer - B ccp = fcc. |
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| 597. |
The arranegement `ABC, ABC, ABC …….` is referred asA. cubic close packingB. tetrahedral close packingC. octahedral close packingD. hexagonal close packing |
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Answer» Correct Answer - A ABC- ABC type arrangement is refered as CCP. |
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| 598. |
The one that is extensively used as a piezoelectric material isA. tridymiteB. amorphous silicaC. quartzD. mica |
| Answer» Correct Answer - C | |
| 599. |
Which of the following does not adopt hcp structure ?A. BeB. MgC. FeD. Mo |
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Answer» Correct Answer - C Iron has ccp structure. |
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| 600. |
Select the incorrect statement in a CsCl crystal:A. `Cs^(+)` forms a simple cubic lattice, `Cl^(-)` forms a simple cubinc latticeB. `Cl^(-)` occupies body centre of `Cs^(+)`C. `Cs^(+)` occupies body centre of `Cl^(-)`D. It is impossible for `Cl^(-)` to occupy body centre of `Cs^(+)` because the body centre void of `Cs^(+)` is smaller than `Cl^(-)` |
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Answer» Correct Answer - D |
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