Chapter 6 Multiple Choice Questions

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. Select the incorrect statement from the list below.

The largest applications of rare earth elements are in magnets, and in metallurgy and alloys. correct incorrect

The main application of Nd is in lasers. correct incorrect

Large quantities of La and Ce are used in the form of oxides for glass polishing. correct incorrect

Eu, Tb and Y are used in phosphors. correct incorrect

For some applications the choice of lanthanoid element is made on the basis of economic factors. correct incorrect

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. CeO₂ is used as a catalyst to clean up exhaust emissions from motor vehicles. Consider the following statements.
(i) During the catalytic cycle Ce⁴⁺ is reduced to Ce³⁺
(ii) During the catalytic cycle N₂O oxidizes Ce³⁺.
(iii) CeO₂ acts as a store for O₂.
(iv) CeO₂ is always used in its pure state in catalytic converters.
Now select the correct statement from the list below.

(i) and (ii) are the only correct statements correct incorrect

(iii) and (iv) are the only correct statements correct incorrect

all the statements are correct correct incorrect

(i), (ii) and (iii) are correct correct incorrect

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. Consider the following statements about rare earth magnets.
(i) Nd is the major component of neodymium magnets.
(ii) Most lanthanoid metals are ferromagnetic at room temperature.
(iii) Rare earth magnets contain ferromagnetic d-transition metals.
(iv) The magnet in typical wind turbine contains >600 kg of Nd.
(v) Rare earth magnets contain lanthanoid metals with anisotropic electron distributions.
(vi) Rare earth magnets can be used for holding dentures in place.
Now select the correct statement from the list below.

(iii), (iv), (v) and (vi) are correct. correct incorrect

All the statements are correct. correct incorrect

(ii), (iii), (iv) and (v) are correct. correct incorrect

(i), (iv) and (v) are correct. correct incorrect

(i), (ii), (iii) and (v) are correct. correct incorrect

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. Consider the following statements about MRI contrast agents:
(i) Gd³⁺ is used because it causes shifting of ¹H NMR resonances of water
(ii) Most MRI contrast agents use polyaminocarboxylates or their derivatives as ligands
(iii) Gd³⁺(aq) is a suitable contrast agent for MRI of living systems
(iv) Neutral complexes are preferred as they have less osmotic effect than salts
(v) MRI contrast agents work by increasing ¹H NMR relaxation times
Now select the correct statement below:

(ii) and (iv) only are correct correct incorrect

all of the statements are correct correct incorrect

(i), (iii) and (iv) are correct correct incorrect

(ii), (iv) and (v) are correct correct incorrect

none of the statements is correct correct incorrect

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. Select the incorrect statement about lanthanoid phosphors from the list below.

Eu²⁺ is used in blue phosphors. correct incorrect

Eu³⁺ is used in red phosphors. correct incorrect

The colour of Eu²⁺ emission can be changed by changing the host matrix. correct incorrect

Eu³⁺ is excited via a charge transfer transition from the host lattice. correct incorrect

Tb³⁺ produces green emission via direct f-f excitation. correct incorrect

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. Consider the following statements about the use of uranium in nuclear reactors.
(i) ²³⁸U is the main fissile isotope of U.
(ii) ²³⁵U is the main fissile isotope of U.
(iii) Fission of ²³⁵U results in net consumption of one neutron.
(iv) Fission of ²³⁵U results in net production of at least one neutron.
(v) H₂O is used only as a coolant in a pressurized water reactor.
(vi) ²³⁸U is the major isotope of U in nuclear fuels.
(vii) The initial fission products from ²³⁵U are extremely long-lived.
Now select the correct statement from the list below.

(i), (iii), (vi) and (vii) are correct. correct incorrect

(ii), (iv) and (vii) are correct correct incorrect

(ii), (iv) and (vi) are correct correct incorrect

(iii), (v) and (vi) are correct correct incorrect

(i), (v) and (vi) are correct correct incorrect

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. Consider the following statements about ²³⁹Pu and nuclear reactors.
(i) ²³⁹Pu is formed due to neutron capture by ²³⁵U.
(ii) ²³⁹Pu is formed due to neutron capture by ²³⁸U.
(iii) Fission of ²³⁹Pu requires 'thermal' neutrons.
(iv) Liquid sodium is used as a moderator in fast breeder reactors
(v) Mixed oxide fuel (MOX) is produced by reprocessing spent nuclear fuel rods.
Now select the correct statement from the list below.

(ii) and (v) are correct correct incorrect

(i) and (iii) are correct correct incorrect

(ii), (iii) and (iv) are correct correct incorrect

(i), (iv) and (v) are correct correct incorrect

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. Select the incorrect statement about lanthanoid triflates (Ln(OTf)₃) from the list below.

Ln(OTf)₃ are less water tolerant than BCl₃. correct incorrect

Ln(OTf)₃ form very labile Ln-ligand bonds. correct incorrect

Yb(OTf)₃ is more Lewis acidic than Lu(OTf)₃. correct incorrect

Low loadings of Ln(OTf)₃ are required in catalytic reactions. correct incorrect

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. Select the incorrect statement about Nd lasers from the list below.

The Nd:YAG laser is the most widely used IR laser. correct incorrect

The Nd:YAG laser is an example of a three-level laser.. correct incorrect

The terminal state of the Nd:YAG laser is not the ground state of Nd³⁺. correct incorrect

The ground state of Nd³⁺ is ⁴I_9/2. correct incorrect

Approximately 1% of Y³⁺ ions in Y₃Al₅O₁₂ are replaced with Nd³⁺ in the Nd:YAG laser. correct incorrect

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. Select the correct statement about organocerium reagents.

Organocerium reagents are more selective for addition to carbonyls than organo lithium reagents correct incorrect

Organocerium reagents have the general formula CeCl₂R correct incorrect

Organocerium reagents are unsuitable for addition to enolizable substrates correct incorrect

Organocerium reagents are powerful Lewis acids correct incorrect