Metal Excess Defect

Q.

In metal excess defect, anions all missed from their lattice sites and they are occupied by electrons to maintain electrical neutrality. These sites occupied by electrons are called F-centers.

What is the effect of metal excess defect on density of the crystal?

1. Increases

2. Does Not have any effect

3. Decreases

4. Decreases, then increases

Q.

Paragraph :In metal excess defect, anions all missed from their lattice sites and they are occupied by electrons to maintain electrical neutrality. These sites occupied by electrons are called F-centers.

Question: The colour of NaCl changes when heated in sodium vapour due to

1. Excess of sodium in the crystal

2. Electrons in the voids

3. Excess of chlorine in the crystal

4. Deficiency of sodium in the crystal

Q.

Paragraph :In metal excess defect, anions all missed from their lattice sites and they are occupied by electrons to maintain electrical neutrality. These sites occupied by electrons are called F-centers.

Question: In metal excess defect

1. anions miss from their lattice points

2. Cations miss from their lattice points

3. Both cations and anions miss from their lattice points

4. Extra anions are doped

Q. Assertion: Anion vacancies in alkali halides are produced by heating the alkali halide crystals with alkali metal vapour.
Reason: Electrons trapped in anion vacancies are referred to as F-centers.

1. If both assertion and reason are true and the reason is the correct explanation of the assertion.
2. If assertion is true but reason is false.
3. If the assertion and reason both are false.
4. If both assertion and reason are true but reason is not the correct explanation of the assertion.

Q.

The apperance of colour in solid alkali metal halides is generally due to

1. Interstitial positions

2. F- center

3. Frenkel defect

4. Schottky defect

Q. Which of the following defect produces F-centres ?

1. Metal excess defect
2. Scottky defect
3. Metal deficiency defect
4. Vacancy defect

Q. Cementite is:

1. A compound resembling cement
2. An alloy of $Fe$ and $Cr$
3. Interstitial compound of iron and carbon
4. An ore of iron

Q.

Those elements impart colour to the flame on heating in it, the atoms of which require the low energy of the ionization (i.e., absorb energy in group visible region of the spectrum). The elements of which of the following groups will impart colour to the flame?
(a) 2 (b) 13 (c) 1 (d) 17

Q.

An excess of potassium ions makes KCL crystals appear violet or lilac colour since ................

(a) some of the anionic sites are occupied by an unpaired electron

(b) some of the anionic sites are occupied by a pair of electrons

(c) there are vacancies at some anionic sites

(d) F-centres are created which impart colors to the crystals

Q.

Why does table salt, NaCl sometimes appear yellow in colour?