← Back to topic
Vidaara.orgClass 12 · Chemistry
CodeVID-C12-01-T3-01
Assignment — Imperfections & Properties
Chapter: The Solid State
Topic: Imperfections & Properties
Maximum Marks: 30
Time: 60 minutes
Name: ____________________ Roll No.: __________ Date: ____________

General Instructions

  • All questions are compulsory.
  • Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
  • Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions 5 × 1 = 5 marks
1.
The Frenkel defect affects the density of a crystal by:
  • A.increasing it
  • B.decreasing it
  • C.no change
  • D.doubling it
2.
A p-type semiconductor is made by doping Si with:
  • A.phosphorus
  • B.arsenic
  • C.boron
  • D.antimony
3.
Substances with all paired electrons are:
  • A.paramagnetic
  • B.diamagnetic
  • C.ferromagnetic
  • D.ferrimagnetic
4.
$\text{Fe}_{0.95}\text{O}$ is an example of a:
  • A.Schottky defect
  • B.Frenkel defect
  • C.metal deficiency defect
  • D.metal excess defect
5.
F-centres are formed by:
  • A.electrons trapped in anion vacancies
  • B.extra cations
  • C.missing electrons
  • D.interstitial anions
Section B — Short Answer (2 marks) 3 × 2 = 6 marks
6.
Differentiate between Schottky and Frenkel defects on the basis of density.
7.
Distinguish n-type and p-type semiconductors by their charge carriers.
8.
Define ferromagnetic and antiferromagnetic substances.
Section C — Short Answer (3 marks) 2 × 3 = 6 marks
9.
Explain metal excess and metal deficiency non-stoichiometric defects with one example each.
10.
How does temperature affect the conductivity of metals and of semiconductors?
Section D — Long Answer (5 marks) 1 × 5 = 5 marks
11.
Classify point defects into stoichiometric and non-stoichiometric. Describe Schottky, Frenkel, metal excess and impurity defects with examples and their effect on density/properties.

Answer Key

Section A — Multiple Choice Questions
  1. (C) no change
  2. (C) boron
  3. (B) diamagnetic
  4. (C) metal deficiency defect
  5. (A) electrons trapped in anion vacancies
Section B — Short Answer (2 marks)
  1. Schottky lowers density (ions removed); Frenkel keeps density unchanged (ion only displaced to an interstitial site).
  2. n-type carries current by extra electrons (Group-15 dopant); p-type carries current by positive holes (Group-13 dopant).
  3. Ferromagnetic: domains align in the same direction, strong and retained magnetism (Fe). Antiferromagnetic: domains align equally and oppositely, cancelling to zero net moment (MnO).
Section C — Short Answer (3 marks)
  1. Metal excess: anion vacancy filled by a trapped electron (F-centre), e.g. NaCl heated in Na vapour turns yellow. Metal deficiency: a cation is missing and a neighbouring ion takes a higher oxidation state, e.g. $\text{Fe}_{0.95}\text{O}$.
  2. For metals conductivity decreases on heating (greater ionic vibration scatters electrons); for semiconductors conductivity increases on heating (more electrons jump the small band gap).
Section D — Long Answer (5 marks)
  1. Stoichiometric: Schottky (equal cation/anion vacancies, density falls, NaCl) and Frenkel (ion in interstitial site, density unchanged, ZnS). Non-stoichiometric: metal excess (anion vacancy + trapped electron forming F-centres that give colour) and metal deficiency ($\text{Fe}_{0.95}\text{O}$). Impurity: a higher-valent ion such as $\text{Sr}^{2+}$ replaces two $\text{Na}^+$, creating cation vacancies.
Generated by Vidaara.org · Assignment VID-C12-01-T3-01 · vidaara.org