Chemistry NCERT Exemplar Solutions Class 12th Chapter One

47. The correct order of the packing efficiency in different types of unit cells is ________. 

(i) fcc <  bcc <  simple cubic 

(ii) fcc > bcc > simple cubic 

(iii) fcc < bcc > simple cubic 

(iv) bcc <  simple > cubic 

46. A ferromagnetic substance becomes a permanent magnet when it is placed in a magnetic field because ________. 

(i) All the domains get oriented in the direction of magnetic field. 

(ii) All the domains get oriented in the direction opposite to the direction of magnetic field. 

(iii) Domains get oriented randomly. 

(iv) Domains are not affected by magnetic field. 

45. Which of the following is not true about the ionic solids? 

(i) Bigger ions form the close packed structure. 

(ii) Smaller ions occupy either the tetrahedral or the octahedral voids depending upon their size. 

(iii) Occupation of all the voids is not necessary. 

(iv) The fraction of octahedral or tetrahedral voids occupied depends upon the radii of the ions occupying the voids. 

44. Which of the following statements is not true? 

(i) Paramagnetic substances are weakly attracted by magnetic field. 

(ii) Ferromagnetic substances cannot be magnetised permanently. 

(iii) The domains in antiferromagnetic substances are oppositely oriented with respect to each other. 

(iv) Pairing of electrons cancels their magnetic moment in the diamagnetic substances. 

43. Silicon doped with electron-rich impurity forms ________. 

(i) P-type semiconductor 

(ii) N-type semiconductor

(iii) Intrinsic semiconductor 

(iv) Insulator 

42. Which kind of defects are introduced by doping? 

(i) Dislocation defect 

(ii) Schottky defect 

(iii) Frenkel defects 

(iv) Electronic defects 

41. What is the coordination number in a square close packed structure in two dimensions? 

(i) 2 

(ii) 3 

(iii) 4 

(iv) 6

40. In which of the following structures coordination number for cations and anions in the packed structure will be same? 

(i) Cl ion form fcc lattice and Na⁺ ions occupy all the octahedral voids of the unit cell. 

(ii) Ca²⁺ions form fcc lattice and  F ions occupy all the eight tetrahedral voids of the unit cell. 

(iii) O² ions form fcc lattice and Na⁺ions occupy all the eight tetrahedral voids of the unit cell. 

(iv) S²ions form fcc lattice and Zn²⁻ ions go into the alternate tetrahedral voids of the unit cell. 

39. Which of the following statement is not true about the hexagonal close packing? 

(i) The coordination number is 12. 

(ii) It has 74% packing efficiency. 

(iii) Tetrahedral voids of the second layer are covered by the spheres of the third layer. 

(iv) In this arrangement spheres of the fourth layer are exactly aligned with those of the first layer. 

38. The percentage of empty space in a body centred cubic arrangement is ________. 

(i) 74 

(ii) 68 

(iii) 32 

(iv) 26