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The Solid State — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryThe Solid State4 Marks
Question
Read the passage given below and answer the following questions:
Most important crystal lattices are the simple cubic, body centred cubic and face centred cubic. In simple cubic lattice, all the atoms are present at all the corners of the cube. In body-centred cubic lattice, atoms are present at all the corners and at the body-centre. In face-centred cubic lattice, atoms are present at the corners and at the centers of all six faces. In the formation of crystals, the constituent particles get closely packed together. The closely packed arrangement is that in which maximum available space is occupied, leaving minimum vacant space. The most efficient close packing, can be achieved in two ways, one which is called hexagonal close packing.(hcp) and the other, cubic close packing (ccp or fcc)
In these questions (Q. No. i-iv) a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
  1. Assertion and reason both are correct statements, and reason is correct explanation for assertion.
  2. Assertion and reason both are correct statements, but reason is not correct explanation for assertion.
  3. Assertion is correct statement, but reason is wrong statement.
  4. Assertion is wrong statement, but reason is correct statement.
  1. Assertion: Face centred cubic cell has $4$ atoms per unit cell.
Reason: ln fee unit cell, there are $8$ atoms at the corners and $ 6$ atoms at face centres
  1. Assertion: CsCl has body-centred cubic arrangement.
Reason: CsCl has one $Cs^+$ ion and $8$ $CI^-$ ions in its unit cell.
  1. Assertion: fcc and hcp have same packing efficiency.
Reason: bcc and fcc both have same number of atoms per unit cell and same arrangement.
  1. 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.
  1. Assertion: The packing efficiency is maximum for the fee structure.
Reason: The coordination number is $12$ in fcc structures.
✓

Answer

  1. (a) Assertion and reason both are correct statements, and reason is correct explanation for assertion.
  2. (a) Assertion and reason both are correct statements, and reason is correct explanation for assertion.
Explanation:

CsCl has body-centred cubic arrangement in which atoms are present at the corners and at the body center. Now, $Cs^+$ is present at the body centre while$ Cl$ ions are present at the corners. So, number of $Cl^- ions = 8$ Number of $Cs^+ ion = 1$
  1. (c) Assertion is correct statement, but reason is wrong statement.
Explanation:

fcc and hcp both have $74\%$ packing efficiency. In bee there are $2$ atoms per unit cell while in fee there are $4$ atoms per unit cell and both have different arrangements.
  1. (a) Assertion and reason both are correct statements, and reason is correct explanation for assertion.
  2. (b) Assertion and reason both are correct statements, but reason is not correct explanation for assertion.
Explanation:

The no. of atoms in fee structure is $4$ per unit cell, which provides a maximum efficiency as $74\%.$

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The progress of the reaction, $\text{A}\rightleftharpoons\text{nB}$ with time is represented in the following figure:

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  1. 1
  2. 2
  3. 3
  4. 4
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  1. 0.6M
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  3. 0.3M
  4. 2.4M
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  2. $0.2 mol ~L^{-1}hr^{-1}$
  3. $0.4 mol ~L^{-1}hr^{-1}$
  4. $0.8 mol ~L^{-1}hr^{-1}$
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