# NEET Chemistry The Solid State Questions Solved

BOARD

(a) Some of the glass objects recovered from ancient monuments look milky instead of being transparent. Why?

(b) Iron (II) oxide has a cubic structure and each side of the unit cell is 5$\stackrel{\circ }{A}$. If density of the oxide is 4 g cm-3, calculate the number of Fe2+ and O2- ions present in each unit cell.

[Atomic mass : Fe = 56 u, O = 16 u; Avogadro's number = 6.023$×$1023 mol-1]

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Concept Questions :-

Density/Formula/packing fraction/ Semiconductors

(a) Some of the glass objects found from ancient monuments look to be milky in appearance because of crystallisation of glass.

(b) Volume of unit cell = a3 = (5$\stackrel{\circ }{A}$) = (5$×$10-8)3

= 1.25$×$10-22 cm

Density of FeO = 4g cm-3

Mass of unit cell = Volume $×$ Density

= 1.25$×$10-22$×$4 g

= 5$×$10-22 g

Mass of FeO molecule per unit cell

=    = 4.19 $\approx$ 4

Thus 4Fe+2, 4O-2 will be present in each unit cell.

Difficulty Level:

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