8. Transition and inner transition element 12th chem CET MCQ
[2013] 1. Which of the following ion is diamagnetic?
Correct Answer: (A) Sc3+
Solution: Sc (Z=21) has the configuration [Ar] 3d¹ 4s². In the +3 oxidation state, it loses 3 electrons to become [Ar] 3d⁰. Since there are no unpaired electrons, it is diamagnetic[cite: 10].
[2014] 2. Select the coloured compound amongst the following. (Atomic no. Ti=22, Cr=24 Cu=29, Zn=30)
Correct Answer: (B) CrCl3
Solution: Colour in transition metal compounds is due to d-d transitions[cite: 20]. Cr³⁺ (3d³) has unpaired electrons, making it coloured[cite: 30]. Ti⁴⁺ (3d⁰), Zn²⁺ (3d¹⁰), and Cu⁺ (3d¹⁰) do not have unpaired electrons in the d-subshell.
[2015] 3. Potassium dichromate is a good oxidizing agent, in acidic medium the oxidation state of chromium changes by:
Correct Answer: (B) 3
Solution: In acidic medium, Cr₂O₇²⁻ (+6 state) is reduced to Cr³⁺ (+3 state)[cite: 40, 49]. The change in oxidation state is 6 - 3 = 3[cite: 56].
[2015] 4. The only radioactive element among the lanthanoids is:
Correct Answer: (C) promethium
Solution: Promethium (Pm) is the only radioactive element in the lanthanoid series[cite: 62, 81].
[2016] 5. Identify the metal that forms colourless compounds (in its +3 oxidation state).
Correct Answer: (D) Scandium (Z=21)
Solution: Sc³⁺ has a 3d⁰ configuration (noble gas core)[cite: 108]. Because it has no electrons in the d-orbital, d-d transitions are impossible, resulting in colourless compounds[cite: 90].
[2016] 6. How is sodium chromate converted into sodium dichromate in the manufacture of potassium dichromate from chromite ore?
Correct Answer: (A) By the action of concentrated sulphuric acid
Solution: In the industrial process, sodium chromate solution is acidified with concentrated sulphuric acid to convert it into sodium dichromate[cite: 8, 18].
[2017] 7. Which among the following is NOT a mineral of iron?
Correct Answer: (B) Magnesite
Solution: Magnesite is a mineral of magnesium (MgCO₃)[cite: 48]. Haematite, Magnetite, and Siderite are all iron minerals[cite: 38, 46, 52, 54].
[2018] 8. Identify the oxidation states of titanium (Z=22) and copper (Z=29) in their colourless compounds.
Correct Answer: (C) Ti4+, Cu1+
Solution: Ti⁴⁺ is 3d⁰ and Cu¹⁺ is 3d¹⁰[cite: 84, 85]. Both lack unpaired electrons for d-d transitions, making their compounds colourless[cite: 66, 70].
[2018] 9. The most basic hydroxide from following is:
Correct Answer: (D) La(OH)3 (Z=57)
Solution: As the atomic number increases in the lanthanoid series, the ionic radius decreases (lanthanoid contraction), causing the basicity of hydroxides to decrease[cite: 92]. Thus, La(OH)₃ is the most basic[cite: 110].
[2019] 10. The spin only magnetic moment of Ni2+ (Z=28) in aqueous solution is:
Correct Answer: (B) 2.84 BM
Solution: Ni²⁺ (3d⁸) has 2 unpaired electrons[cite: 115]. Using μ = √[n(n+2)], we get √[2(2+2)] = √8 ≈ 2.84 BM[cite: 114, 123].
[2019] 11. Percentage of carbon in steel is:
Correct Answer: (A) 0.2 to 2%
Solution: Steel is an alloy of iron containing approximately 0.2% to 2% carbon[cite: 131, 133].
[2019] 12. Which among the following elements is radioactive?
Correct Answer: (D) Pm
Solution: Promethium (Pm) is the radioisotope in the lanthanoid series[cite: 150, 153].
[2019] 13. Which among the following elements has completely filled 4f subshell?
Correct Answer: (C) Yb (Z=70)
Solution: Ytterbium (Yb, Z=70) has the electronic configuration [Xe] 4f¹⁴ 6s², showing a completely filled 4f subshell[cite: 157, 162, 172].
[2019] 14. Identify the pair of flux and the slag respectively in the extraction process of iron.
Correct Answer: (A) Limestone and calcium silicate
Solution: In the extraction of iron, limestone (CaCO₃) is used as a flux, which reacts with silica to form slag, calcium silicate (CaSiO₃)[cite: 176, 185, 189].
[2020] 15. Identify CORRECT decreasing order of ionic radii of lanthanoids.
Correct Answer: (C) Ce > Pm > Sm > Gd
Solution: Due to lanthanoid contraction, the ionic radius decreases as the atomic number increases[cite: 203, 207]. The correct order following increasing Z (Ce=58, Pm=61, Sm=62, Gd=64) is Ce > Pm > Sm > Gd[cite: 222].
[2020] 16. Which among the following elements is a soft element as compared to others?
Correct Answer: (A) Zn
Solution: Zinc (Zn) is a relatively soft metal compared to transition metals like Tungsten (W) or Molybdenum (Mo) due to its filled d-shell and weaker metallic bonding[cite: 228, 235].
[2020] 17. Which of the following is a product of first step and is used as reactant in next step for manufacture of K2Cr2O7 from concentrated chromite ore?
Correct Answer: (C) Sodium chromate
Solution: In the first step, chromite ore is roasted with sodium carbonate to produce sodium chromate[cite: 238, 254]. This sodium chromate is then converted into sodium dichromate in the second step[cite: 244].
[2020] 18. Which of the following actinoids exhibits only +3 oxidation state?
Correct Answer: (B) Lr (Z=103)
Solution: Lawrencium (Lr, Z=103), being the last actinoid, exhibits only a stable +3 oxidation state[cite: 261, 269].
[2020] 19. Which among the following sets of elements is present in chalcopyrite?
Correct Answer: (C) Cu, Fe, S
Solution: Chalcopyrite is a copper-iron sulfide mineral with the chemical formula CuFeS₂[cite: 278, 283].
[2020] 20. Which among the following elements possesses one electron in 4s orbital in observed electronic configuration?
Correct Answer: (A) Cu (Z=29)
Solution: Copper (Cu, Z=29) has an exceptional configuration: [Ar] 3d¹⁰ 4s¹ to achieve a stable fully-filled d-subshell[cite: 285, 290].
[2020] 21. Which among the following elements does NOT form oxocation?
Correct Answer: (B) Lu
Solution: Actinoids like U, Np, and Pu form stable oxocations (e.g., UO₂²⁺) due to their high oxidation states[cite: 297]. Lutetium (Lu) is a lanthanoid and typically only forms M³⁺ ions without oxygen[cite: 297].
[2021] 22. Which among the following statements about common properties of d-block elements is NOT true?
Correct Answer: (A) These are bad conductors of heat and electricity.
Solution: d-block elements are transition metals, which are characterized by being excellent conductors of heat and electricity[cite: 130, 134].
[2021] 23. Which among the following lanthanoid hydroxides is the strongest base?
Correct Answer: (A) La(OH)3
Solution: Basicity decreases from La(OH)₃ to Lu(OH)₃ due to the decrease in ionic size (Lanthanoid contraction)[cite: 160]. Therefore, La(OH)₃ is the strongest base[cite: 160].
[2021] 24. Identify the last element in lanthanoid series.
Correct Answer: (C) Lu
Solution: The lanthanoid series starts with Lanthanum (or Cerium depending on definition) and ends with Lutetium (Z=71)[cite: 171, 178].
[2021] 25. Identify the element having smallest atomic radius from following.
Correct Answer: (D) Tm
Solution: In the lanthanoid series, atomic radius decreases as atomic number increases[cite: 182, 186]. Thulium (Tm) has the highest atomic number among the choices, thus the smallest radius[cite: 197].
[2021] 26. Which among the following elements has completely filled 4d-orbital?
Correct Answer: (B) Cd
Solution: Cadmium (Cd, Z=48) has a completely filled 4d¹⁰ 5s² configuration[cite: 205, 209].
[2021] 27. Select the catalyst used in hydrogenation of ethane.
Correct Answer: (C) Ni (finely divided)
Solution: Finely divided Nickel (Raney Nickel) is a standard catalyst for the hydrogenation of unsaturated hydrocarbons[cite: 214, 230].
[2021] 28. Which among the following cations will NOT form coloured compounds? (Atomic number Cu=29 Ti=22, V=23 Mn=25)
Correct Answer: (C) Cu+
Solution: Cu⁺ has a 3d¹⁰ configuration[cite: 242, 246]. Since the d-orbital is completely filled, d-d transition is not possible, making it colourless[cite: 246].
[2021] 29. What is the value of spin only magnetic moment found in Cu (Z=29) in +2 oxidation state?
Correct Answer: (C) 1.73 BM
Solution: Cu²⁺ has configuration [Ar] 3d⁹, which has 1 unpaired electron[cite: 252]. μ = √[1(1+2)] = √3 ≈ 1.73 BM[cite: 262].
[2021] 30. Which element from following is a soft element?
Correct Answer: (B) Zn
Solution: Zinc is considered a soft metal among the transition elements because all its d-electrons are paired, leading to weaker metallic bonding[cite: 270, 275].
[2022] 31. Identify the outer electronic configuration of first element of first transition series.
Correct Answer: (B) [Ar] 3d1 4s2
Solution: The first element of the first transition series (3d series) is Scandium (Z=21) with configuration [Ar] 3d¹ 4s²[cite: 298, 302].
[2022] 32. Which from following pair of elements have one electron in 5d-subshell in observed electronic configuration?
Correct Answer: (B) Gd (Z=64) and Lu (Z=71)
Solution: Gadolinium ([Xe] 4f⁷ 5d¹ 6s²) and Lutetium ([Xe] 4f¹⁴ 5d¹ 6s²) both have one electron in the 5d-subshell to maintain stable f-subshell half/full-fill configurations[cite: 310, 311, 312].
[2022] 33. Which among the following is an actinoid element?
Correct Answer: (A) Pa
Solution: Protactinium (Pa) belongs to the actinoid series (5f series)[cite: 323, 330]. Lu, Gd, and Pr are lanthanoids.
[2022] 34. Identify the element having smallest atomic radius from following.
Correct Answer: (D) Tm
Solution: Radius decreases across the series due to Lanthanoid contraction; thus Thulium (Tm), being the furthest along among choices, is the smallest[cite: 335, 345].
[2022] 35. Identify non-radioactive element from following.
Correct Answer: (D) Nd
Solution: Neodymium (Nd) is a stable lanthanoid, while Californium (Cf), Uranium (U), and Neptunium (Np) are radioactive actinoids[cite: 349, 356].
[2022] 36. What is the number of unpaired electrons present in f-orbital at +3 oxidation state of Lu (Z=71)?
Correct Answer: (C) 0
Solution: Lu³⁺ has configuration [Xe] 4f¹⁴. Since the f-orbital is completely filled, there are zero unpaired electrons[cite: 364, 369, 377].
[2022] 37. What is the position of copper in modern periodic table?
Correct Answer: (B) Period-4, Group-11
Solution: Copper (Z=29) is a transition metal located in the 4th period and 11th group[cite: 384, 396].
[2022] 38. Which from following alloys is used for ultra-high speed flight?
Correct Answer: (D) Titanium alloy
Solution: Titanium alloys are valued for their strength, light weight, and heat resistance, making them ideal for aerospace and high-speed flight[cite: 404, 422].
[2022] 39. What is the number of unpaired electrons present in Sc3+ and Zn2+ ions respectively?
Correct Answer: (A) 0,0
Solution: Sc³⁺ is 3d⁰ and Zn²⁺ is 3d¹⁰. Both have no unpaired electrons[cite: 419, 431, 439].
[2022] 40. Which among the following is weakest base?
Correct Answer: (D) Lu(OH)3
Solution: Due to Lanthanoid contraction, basicity decreases as atomic number increases. Lu is the last element, so its hydroxide is the weakest base among these[cite: 441, 459].
[2022] 41. What is the position of titanium in modern periodic table?
Correct Answer: (A) Period-4, Group-4
Solution: Titanium (Z=22) has the electronic configuration [Ar] 3d² 4s². It belongs to the 4th period and Group 4 of the d-block.
[2022] 42. Which element from 3d transition series is at the top having highest melting point when a graph of atomic number and their melting points is plotted?
Correct Answer: (B) Cr
Solution: In the 3d series, Chromium (Cr) has the highest melting point due to the maximum number of unpaired electrons (3d⁵ 4s¹) available for metallic bonding.
[2022] 43. What is the general electronic configuration of elements of 4th transition series?
Correct Answer: (B) [Rn] 6d1-10 7s2
Solution: The 4th transition series (6d series) starts after Radon (Rn). Its general configuration involves the filling of the 6d subshell.
[2022] 44. Which element from following has half-filled f-orbital in +3 oxidation state?
Correct Answer: (C) Cm (Z=96)
Solution: Curium (Cm, Z=96) has configuration [Rn] 5f⁷ 6d¹ 7s². In the +3 state, it becomes [Rn] 5f⁷, which is a stable half-filled configuration.
[2022] 45. Which among the following is an actinoid element?
Correct Answer: (A) Pa
Solution: Protactinium (Pa) is a member of the actinoid series. The others are lanthanoids.
[2022] 46. Which among the following lanthanoids forms most stable +2 oxidation state?
Correct Answer: (D) Eu (Z=63)
Solution: Europium (Eu) forms a stable +2 state because Eu²⁺ has a [Xe] 4f⁷ configuration, which is exactly half-filled and highly stable.
[2022] 47. Identify the element with smallest ionic radius in +3 oxidation state from following.
Correct Answer: (D) Lu
Solution: Ionic radius decreases across the lanthanoid series. Lutetium (Lu) is the final element, so Lu³⁺ has the smallest ionic radius among the choices.
[2022] 48. What is the number of unpaired electrons present in Fe (Z=26) in +3 state?
Correct Answer: (C) 5
Solution: Fe (Z=26) is [Ar] 3d⁶ 4s². Fe³⁺ is [Ar] 3d⁵. In the d-subshell, 5 electrons occupy 5 orbitals singly, resulting in 5 unpaired electrons.
[2022] 49. Which among the following statements is NOT true about lanthanoids?
Correct Answer: (B) Basicity of hydroxides of lanthanoids increases as the atomic number increases.
Solution: Basicity actually decreases as atomic number increases due to the decrease in ionic size (lanthanoid contraction).
[2022] 50. Which element from following has lowest volatility?
Correct Answer: (B) Cr
Solution: Chromium has high metallic bond strength due to unpaired electrons, leading to low volatility (high boiling point). Zn, Cd, and Hg have filled d-shells and are more volatile.
[2022] 51. Which among the following series of elements is also called as rare earth element?
Correct Answer: (A) Lanthanoid series
Solution: The lanthanoid series elements are traditionally known as rare earth elements.
[2022] 52. Identify lanthanoid element from following.
Correct Answer: (A) Promethium
Solution: Promethium (Pm) is a lanthanoid. Thorium and Neptunium are actinoids; Vanadium is a d-block element.
[2023] 53. Find the value of spin only magnetic moment for chromium cation in +2 state.
Correct Answer: (B) 4.90 BM
Solution: Cr²⁺ is 3d⁴, which has 4 unpaired electrons (n=4). μ = √[4(4+2)] = √24 ≈ 4.90 BM.
[2023] 54. Which among the following elements does NOT exhibit ferromagnetic properties?
Correct Answer: (A) Cr
Solution: Fe, Co, and Ni are classic ferromagnetic materials. Chromium is antiferromagnetic.
[2023] 55. Which from following is a molecular formula of siderite?
Correct Answer: (C) FeCO3
Solution: Siderite is an iron carbonate mineral with the formula FeCO₃.
[2023] 56. Identify nonferrous alloy from following.
Correct Answer: (C) Brass
Solution: Brass is an alloy of Copper and Zinc; it does not contain iron (nonferrous).
[2023] 57. Which from following statements regarding transition elements is NOT correct?
Correct Answer: (C) 5d series consists of all elements from lanthanum to mercury of periodic table.
Solution: The 5d series is interrupted by the 4f (lanthanoid) series. It does not simply contain "all" elements in that span consecutively in the d-block.
[2023] 58. Identify the element from following having six unpaired electrons in observed electronic configuration?
Correct Answer: (C) Cr
Solution: Cr (Z=24) has the configuration [Ar] 3d⁵ 4s¹. This provides 5 + 1 = 6 unpaired electrons.
[2023] 59. Which element from the following possesses half-filled d-orbitals either in expected or in observed electronic configuration?
Correct Answer: (B) Mn
Solution: Manganese (Mn, Z=25) has a 3d⁵ 4s² configuration, where the 3d subshell is exactly half-filled.
[2023] 60. Which from following elements exhibits highest spin only magnetic moment in +3 state?
Correct Answer: (A) Cr
Solution: Cr³⁺ is 3d³ (n=3). V³⁺ is 3d² (n=2), Ti³⁺ is 3d¹ (n=1), and Sc³⁺ is 3d⁰ (n=0). Cr³⁺ has the highest n and thus highest μ.
[2023] 61. Which element from following will have highest number of unpaired electrons in +2 oxidation state?
Correct Answer: (B) Cr (Z=24)
Solution: Cr²⁺ has a 3d⁴ configuration, which gives 4 unpaired electrons. Cu²⁺ has 1, V²⁺ has 3, and Ti²⁺ has 2.
[2023] 62. Which of the following metals is used as catalyst in manufacture of sulphuric acid by contact process?
Correct Answer: (B) Platinum
Solution: Platinum was traditionally used as the catalyst for the oxidation of sulfur dioxide in the contact process.
[2023] 63. Which of the following elements is doped with to obtain fibre amplifiers for optical fibre communication system?
Correct Answer: (C) Er
Solution: Erbium (Er) is used in Erbium-Doped Fibre Amplifiers (EDFAs) to amplify light signals in long-distance communication.
[2023] 64. Identify lanthanoid element from following.
Correct Answer: (A) Eu
Solution: Europium (Eu) belongs to the lanthanoid series. Curium, Americium, and Neptunium are actinoids.
[2023] 65. What is the calculated value of spin only magnetic moment in terms of BM if only one unpaired electron is present in a species?
Correct Answer: (D) 1.73
Solution: Using the formula μ = √[n(n+2)], where n=1, μ = √3 ≈ 1.73 BM.
[2023] 66. What is the position of transition elements from Sc to Zn in long form of periodic table?
Correct Answer: (B) Group 3 to 12, period-4
Solution: The 3d transition series starts at Group 3 (Scandium) and ends at Group 12 (Zinc) in the 4th period.
[2023] 67. Which element from following does NOT exhibit spin only magnetic moment in +3 state?
Correct Answer: (A) Sc
Solution: Sc³⁺ has a 3d⁰ configuration. Since there are no unpaired electrons, the spin-only magnetic moment is zero.
[2023] 68. Which from following cations in their respective oxidation states develops colourless aqueous solution?
Correct Answer: (D) Cu+
Solution: Cu⁺ has a 3d¹⁰ configuration. With a completely filled d-subshell, d-d transitions are not possible, making the solution colourless.
[2023] 69. What is the numerical value of spin only magnetic moment of copper in +2 state?
Correct Answer: (B) 1.73
Solution: Cu²⁺ has a 3d⁹ configuration (1 unpaired electron). μ = √[1(3)] ≈ 1.73 BM.
[2023] 70. Which from following elements exhibits ferromagnetic properties?
Correct Answer: (B) Co
Solution: Iron, Cobalt, and Nickel are transition metals that show strong ferromagnetism.
[2023] 71. What is the number of elements present in each series of transition element?
Correct Answer: (B) 10
Solution: Each transition series involves the filling of a d-subshell, which has 5 orbitals and can accommodate 10 elements.
[2023] 72. Which from following series of elements is CORRECTLY arranged according to their decreasing order of ionization enthalpy (IE1)?
Correct Answer: (A) Zn > Fe > Cr > Sc
Solution: Ionization enthalpy generally increases across a period from left to right. Therefore, Zn has the highest and Sc has the lowest value among these.
[2023] 73. Which from following statements regarding transition elements is NOT correct?
Correct Answer: (B) Transition elements are more electropositive than elements of group 1 and group 2.
Solution: This statement is false; Group 1 (Alkali) and Group 2 (Alkaline Earth) metals are the most electropositive elements.
[2023] 74. What is the total number of unpaired electrons in observed configuration of elements present at group-11 and period-4 in periodic table?
Correct Answer: (A) 1
Solution: The element is Copper (Cu). Its observed configuration is [Ar] 3d¹⁰ 4s¹, which has only 1 unpaired electron (in the 4s orbital).
[2023] 75. Identify the element if its expected and observed electronic configurations are represented respectively as [Ar] 3d⁴ 4s² and [Ar] 3d⁵ 4s¹.
Correct Answer: (D) Cr
Solution: Chromium (Z=24) shifts one electron from the 4s to the 3d orbital to achieve the stability of a half-filled d-subshell.
[2023] 76. What is the value of spin only magnetic moment of Sc (Z=21) in +3 oxidation state?
Correct Answer: (C) 0.0 BM
Solution: Sc³⁺ has a 3d⁰ configuration. With no unpaired electrons, the magnetic moment is 0.0 BM.
[2023] 77. Identify ferrous alloy from following.
Correct Answer: (D) Nickel-steel
Solution: Ferrous alloys are those where iron is the main component. Nickel-steel is an alloy primarily composed of iron and nickel.
[2023] 78. Identify actinoid element from following.
Correct Answer: (D) Plutonium
Solution: Plutonium is a radioactive element that is part of the actinoid series. Lutetium and Europium are lanthanoids.
[2023] 79. Identify the element if its electronic configuration is represented as [Ar] 3d¹⁰ 4s².
Correct Answer: (D) Zn
Solution: Zinc (Z=30) has the ground state configuration [Ar] 3d¹⁰ 4s².
[2023] 80. What is the number of unpaired electrons in Mn3+?
Correct Answer: (C) 4
Solution: Mn (Z=25) is [Ar] 3d⁵ 4s². Mn³⁺ loses three electrons to become [Ar] 3d⁴, resulting in 4 unpaired electrons.
[2023] 81. Identify the correct decreasing order of atomic radii from following.
Correct Answer: (B) Th > Pa > U > Np
Solution: Similar to lanthanoids, actinoids exhibit "actinoid contraction." As the atomic number increases (Th=90, Pa=91, U=92, Np=93), the atomic radius decreases. Therefore, Thorium is the largest.
[2023] 82. Identify the element having lowest ionization enthalpy from following.
Correct Answer: (A) Sc
Solution: Ionization enthalpy generally increases from left to right across a transition series due to the increase in effective nuclear charge. Scandium, being the first element of the series, has the lowest value among these.
[2023] 83. Identify inner transition element from the following.
Correct Answer: (C) Samarium
Solution: Inner transition elements belong to the f-block. Samarium (Sm) is a lanthanoid. Cobalt, Copper, and Cadmium are d-block transition elements.
[2023] 84. What is the number of unpaired electrons in divalent cation if atomic number is 25?
Correct Answer: (C) 5
Solution: Z=25 is Manganese (Mn). Configuration is [Ar] 3d⁵ 4s². The divalent cation (Mn²⁺) loses the 4s electrons, leaving 3d⁵, which has 5 unpaired electrons.
[2023] 85. What is the total number of electrons present in (n-1)d and ns orbitals of an element present in 8th group and 4th period?
Correct Answer: (C) 8
Solution: The element is Iron (Fe). Its configuration is [Ar] 3d⁶ 4s². The total number of electrons in the (n-1)d and ns orbitals is 6 + 2 = 8.
[2023] 86. Which from following elements is most stable in +3 state?
Correct Answer: (B) Sc
Solution: Scandium (Sc) is most stable in the +3 state as it achieves a stable noble gas configuration ([Ar] 3d⁰ 4s⁰).
[2024] 87. Identify false statement about transition elements.
Correct Answer: (B) 6d-series includes all elements from Ac (Z≈89) to Cn (Z=112).
Solution: Actinium is the start of the series, but the 5f series (actinoids) interrupts the 6d filling. The statement is technically a generalization that ignores the f-block insertion.
[2024] 88. Identify the element from following having observed electronic configuration 3d¹⁰ 4s¹.
Correct Answer: (A) Cu
Solution: Copper (Z=29) has the exceptional configuration [Ar] 3d¹⁰ 4s¹ to achieve the stability of a fully-filled d-subshell.
[2024] 89. Find the numerical value of magnetic moment produced by Mn2+.
Correct Answer: (C) 5.92
Solution: Mn²⁺ has 5 unpaired electrons (n=5). μ = √[5(5+2)] = √35 ≈ 5.92 BM.
[2024] 90. Identify the pair of elements from following so that both members of it exhibit same value of calculated magnetic moment in their respective oxidation states.
Correct Answer: (B) Ti3+ and Cu2+
Solution: Ti³⁺ has 1 unpaired electron (3d¹). Cu²⁺ also has 1 unpaired electron (3d⁹). Both will have a magnetic moment of 1.73 BM.
[2024] 91. Select a pair of transition elements having completely filled d-orbitals from following.
Correct Answer: (B) Cd and Hg
Solution: Cadmium (4d¹⁰) and Mercury (5d¹⁰) both have completely filled d-subshells in their ground states.
[2024] 92. Which element from following has different electronic configurations in expected and observed states due to extra stability?
Correct Answer: (B) Cr
Solution: Chromium (expected: 3d⁴ 4s², observed: 3d⁵ 4s¹) changes configuration to achieve a more stable half-filled d-subshell.
[2024] 93. Which from following is a mineral of copper?
Correct Answer: (A) Chalcopyrite
Solution: Chalcopyrite (CuFeS₂) is a primary ore/mineral of copper.
[2024] 94. Which from following elements does NOT belong to 3d series?
Correct Answer: (B) Tc
Solution: Technetium (Tc) is in the 4d series (5th period). Mn, Ni, and Co are all in the 3d series (4th period).
[2024] 95. Identify elements present in copper pyrites.
Correct Answer: (D) Fe, Cu, S
Solution: Copper pyrites (Chalcopyrite) has the formula CuFeS₂, containing Copper, Iron, and Sulfur.
[2024] 96. Which from following catalysts is used in the Haber's process for manufacture of ammonia?
Correct Answer: (B) Mo/Fe
Solution: Finely divided Iron (Fe) with Molybdenum (Mo) as a promoter is used as a catalyst in Haber's process.
[2024] 97. Identify the element having smallest ionic size in +3 state from following.
Correct Answer: (D) Lu
Solution: Ionic size decreases across the lanthanoid series. Lutetium (Lu) is the last element, so Lu³⁺ is the smallest.
[2024] 98. Which element from following has half filled 4f orbital at observed ground state?
Correct Answer: (A) Gd
Solution: Gadolinium (Gd, Z=64) has the configuration [Xe] 4f⁷ 5d¹ 6s², where the 4f subshell is exactly half-filled.
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