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The Solid State

Short Answer Type

161. A metal (at. mass = 50) has a bcc crystal structure. The density of the metal is 5.96 g cm^–3. Find the volume of its unit cell?

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162. Calculate the density of silver which crystallizes in a face centred cubic lattice with unit cell length 0.4086 nm (At. mass of Ag = 107.88)

Solution:
We have given that

Unit cell length,
a = 0.40806 nm = 4.086 x 10^-10 m

If fcc lattice the number of atoms per unit cell,
i.e. Z = 4

M for Ag = 107.88 g mol^-1^{$= 1.0788 \times 10^{- 1} kg {mol}^{- 1}$

$N_{A} = 6.023 \times 10^{23}$}

Density of Ag, d =

\frac{ZM}{N_{A} a^{3}}

= \frac{4 \times 1.0788 \times 10^{- 1}}{6.023 \times 10^{23} \times (4.086 \times 10^{- 10})^{3}} = 1.051 \times 10^{4} kg m^{- 3}

Thus the density of silver is 1.051 x 10⁴ kgm^-3

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Long Answer Type

163. An element crystallizes in a structure having a fcc unit cell of an edge 200 pm. Calculate its density if 200 g of this element contains 24 x 10²³ atoms.

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164. An element X with an atomic mass of 60 g/mol has density of 6.23 g/cm^–3. If the edge length of its cubic unit cell is 400 pm, identify the type of cubic unit cell. Calculate the radius of an atom of this element.

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Short Answer Type

165. An atom has fcc crystal whose density is 10 gm^–3 and cell edge is 100 pm. How many atoms are present in its 100 g?

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Long Answer Type

166. Analysis shows that a metal oxide has the empirical formula M_0.98 O_1.00. Calculate the percentage of M²⁺ and M³⁺ ions in this crystal.

Or

In an ionic compound the anion (N) form cubic close type of packing. While the cation (M⁺) ions occupy one third of the tetrahedal voids. Deduce the empirical formula of the compound and the coordination number of (M) ions.

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167. An element E crystallizes in body centred cubic structure. If the edge length of the cell is 1.469 x 10^–10 m and the density is 19.3 g cm^–3, calculate the atomic mass of this element. Also calculate the radius of this element.

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168. Calculate the efficiency of packing in case of a metal crystal for
(i) simple cubic
(ii) body- centred cubic
(iii) face - centred cubic . (With the assumptions that atoms are touching each other).

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Short Answer Type

169. Explain the following with suitable examples:
Ferromagnetism.

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170. Explain the following with suitable examples:
Paramagnetism

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