DIRECTIONS: These are Assertion-Reason type questions. Question contains two statements:Statement-1 (Assertion) and Statement-2 (Reason). Answer these questions from the following four options.
Statement-1 :On heating ferromagnetic or ferrimagnetic substances, they become paramagnetic.
Statement-2 :The electrons change their spin on heating.
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Solution
All magnetically ordered solids (ferromagnetic,ferrimagnetic and antiferromagnetic solids) transform to the paramagnetic state at high temperature due to the randomisation of spins.
In the hexagonal close packed structure of a metallic lattice,the number of nearest neighbours of a metallic atom is
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Solution
Co-ordination number in hcp and ccp arrangement is 12.
In an antifluorite structure, cations occupy
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Solution
In antifluorite structure the oxide ions (anions) form a face-centered cubic array and the metal ions (cations)occupy all the tetrahedral voids. Example: Na2O
In p-type semiconductor, the added impurity to silicon is —-and conduction of electric current is due to the movement of —–
Which set of following characteristics for ZnS crystal is correct?
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Solution
ZnS has cubic close packed (ccp) structure.The S2- ions are present at the corners of the cube and at the centre of each face. Zinc ions occupy half of the tetrahedral sites. Each zinc ion is surrounded by four sulphide ions which are disposed towards the corners of a regular tetrahedron. Similarly, S2-ion is surrounded by four Zn2+ ions.
To get a n- type semiconductor, the impurity to be added to silicon should have which of the following number of valence electrons
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Solution
For n-type, impurity added to silicon should have more than 4 valence electrons.
Which of the following statements about amorphous solids is incorrect ?
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Solution
Amorphous solids are isotropic, because these substances show same properties in all directions.
A crystalline solid
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Solution
In crystalline solid there is perfect arrangement of the constituent particles only at 0 K. As the temperature increases the chance that a lattice site may be unoccupied by an ion increases. As the number of defects increases with temperature solid changes into liquid.
Olive oil when allowed to cool slowly gets solidified and forms a solid over a wide range of temperature. Best description of the solid based on above observation is
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Solution
It can best be described as molecular solid.
A matchbox exhibits
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Solution
Match box exhibits orthorhombic geometry i.e.a ≠ b ≠ c; α = β = γ = 90°