Chemistry 12: Chapter 1 Exemplar Solutions State Solid State Part 7

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V. Assertion and Reason Type

Note: In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.

(i) Assertion and reason both are correct statements and reason is correct explanation for assertion.

(ii) Assertion and reason both are correct statements but reason is not correct explanation for assertion.

(iii) Assertion is correct statement but reason is wrong statement.

(iv) Assertion is wrong statement but reason is correct statement.

Question 69:

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.

Answer: (i)

Question 70:

Assertion: Graphite is a good conductor of electricity however diamond belongs to the category of insulators.

Reason: Graphite is soft in nature on the other hand diamond is very hard and brittle.

Answer: (ii)

Question 71:

Assertion: Total number of octahedral voids present in unit cell of cubic close packing including the one that is present at the body centre, is four.

Reason: Besides the body centre there is one octahedral void present at the centre of each of the six faces of the unit cell and each of which is shared between two adjacent unit cells.

Answer: (iii)

Question 72:

Assertion: The packing efficiency is maximum for the fcc structure.

Reason : The coordination number is in structures.

Answer: (ii)

Question 73:

Assertion: Semiconductors are solids with conductivities in the intermediate range from .

Reason: Intermediate conductivity in semiconductor is due to partially filled valence band.

Answer: (iii)

Question 74:

With the help of a labelled diagram show that there are four octahedral voids per unit cell in a cubic close packed structure.

Answer:

[Hint : Draw structure and discuss]

Question 75:

Show that in a cubic close packed structure, eight tetrahedral voids are present per unit cell.

Answer:

[Hint : Draw structure and discuss]

Question 76:

How does the doping increase the conductivity of semiconductors?

Answer:

See page no. 26 of NCERT textbook for Class XII.

Question 77:

A sample of ferrous oxide has actual formula . In this sample what fraction of metal ions are ions? What type of nonstoichiometric defect is present in this sample?

Answer:

Let the formula of sample be

On looking at the given formula of the compound

... (1)

Total positive charge on ferrous and ferric ions should balance the two units of negative charge on oxygen. Therefore,

... (2)

…..(3)

On subtracting equation (1) from equation (3) we have

On putting the value of y in equation (1) we get,

Fraction of ions present in the sample

Metal deficiency defect is present in the sample because iron is less in amount than that required for stoichiometric composition.

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