Question 1

Although +3 oxidation state is most common in lanthanoids, cerium still shows +4 oxidation state because :

Accepted Answer

The atomic number of Cerium (Ce) is 58. The electronic configuration of Ce is [Xe] 4f^ 1 5d^ 1 6s^ 2 . In +3 oxidation state, the electronic configuration of Ce^ 3+ is [Xe] 4f^ 1 . By losing one more electron, it forms Ce^ 4+ ion. The electronic configuration of Ce^ 4+ is [Xe] 4f^ 0 , which is a highly stable noble gas configuration. Thus, Cerium shows +4 oxidation state because after losing one more electron from +3 state, it acquires 4f^ 0 electronic configuration. Answer: After losing one mor

Question 2

The lanthanide ion having four unpaired electrons is (Given : Atomic numbers of Ce =58, Nd =60, Tb =65 and Ho =67)

Accepted Answer

The general electronic configuration of lanthanide ions Ln ^ 3+ is [ Xe ] 4f^ Z-57 , where Z is the atomic number. For Ho ^ 3+ (Z=67): Number of 4f electrons = 67 - 57 = 10 Configuration is [ Xe ] 4f^ 10 . Since the f-subshell has 7 orbitals, 10 electrons will fill as 3 pairs and 4 unpaired electrons. Number of unpaired electrons = 14 - 10 = 4. For Nd ^ 3+ (Z=60): Number of 4f electrons = 60 - 57 = 3 Configuration is [ Xe ] 4f^ 3 . Number of unpaired electrons = 3. For Ce ^ 3+ (Z=58): Number of

Question 3

The green paramagnetic species formed by heating KMnO_4 at 513 K is

Accepted Answer

When potassium permanganate ( KMnO _4) is heated at 513 K , it decomposes to form potassium manganate, manganese dioxide, and oxygen gas. 2 KMnO _4 513 K K _2 MnO _4 + MnO _2 + O _2 The species K _2 MnO _4 (potassium manganate) is green in color. In K _2 MnO _4, the oxidation state of Mn is +6. The electronic configuration of Mn ^ 6+ is [ Ar ] 3d^1. Since it contains one unpaired electron in the d-orbital, it is paramagnetic in nature. Thus, the green paramagnetic species formed is K _2 MnO _4.

Question 4

The calculated 'spin-only' magnetic moment of Ti ^ 2+ \ (3d^2) is :

Accepted Answer

The atomic number of Ti is 22. Electronic configuration of Ti is [ Ar ] 3d^2 4s^2. Electronic configuration of Ti ^ 2+ is [ Ar ] 3d^2. Number of unpaired electrons, n = 2. Spin-only magnetic moment, = n(n+2) BM . = 2(2+2) = 8 2.84 BM . Answer: 2.84 BM

Question 5

Match List I with List II : List I (Transition metal/compound/complex) List II (Catalytic Role) A. V _2 O _5 I. Preparation of ammonia from N _2/ H _2 mixture B. Fe II. Polymerisation of alkynes C. Pd

Accepted Answer

V _2 O _5 is used as a catalyst in the Contact process for the oxidation of SO _2 to SO _3 during the preparation of H _2 SO _4. Thus, A matches with III. Finely divided Fe is used as a catalyst in the Haber process for the preparation of ammonia from N _2 and H _2 mixture. Thus, B matches with I. PdCl _2 is used as a catalyst in the Wacker process for the oxidation of ethene (referred to as ethyne in the given options) to ethanal. Thus, C matches with IV. Ni complexes are used as catalysts for

Question 6

Given below are two statements : One is labelled as Assertion A and the other is labelled as Reason R . Assertion A : Generally, 3d transition metals have high melting points. Reason R : Involvement o

Accepted Answer

Assertion A is correct because transition metals generally have high melting points due to strong metallic bonding. Reason R is correct and explains Assertion A because the strong metallic bonding in 3d transition metals is attributed to the involvement of a greater number of electrons from the 3d subshell in addition to the 4s electrons in the interatomic metallic bonding. Thus, both A and R are correct and R is the correct explanation of A. Answer: Both A and R are correct and R is the correct

Question 7

Given below are two statements : Statement I : Ferromagnetism is considered as an extreme form of paramagnetism. Statement II : The number of unpaired electrons in a Cr ^ 2+ ion ( Z =24) is the same a

Accepted Answer

Ferromagnetism > Paramagnetism Statement-I is true Cr ^ +2 =3 ~d ^4 4 unpaired electrons Nd ^ +3 =4 f ^3 3 unpaired electrons Statement-II is false.

Question 8

Which of the following set of ions act as oxidising agents?

Accepted Answer

Most stable oxidation state of lanthanoids is +3 Ce ^ 4+ and Tb ^ 4+ will get reduced easily and will be good oxidising agents.

Question 9

The UV-visible absorption bands in the spectra of lanthanoid ions are ' X ', probably because of the excitation of electrons involving ' Y '. The ' X ' and ' Y ', respectively, are :

Accepted Answer

In lanthanoids, absorption bands are narrow because of excitation within f-level.

Question 10

The oxidation states not shown by Mn in given reaction is : 3 MnO _4^ 2- +4 H ^ + 2 MnO _4^ - + MnO _2+2 H _2 O A. +6 B. +2 C. +4 D. +7 E. +3 Choose the most appropriate answer from the options given

Accepted Answer

In the following reaction 3 MnO _4^ 2- +4 H ^ + 2 MnO _4^ - + MnO _2+2 H _2 O So +2 and +3 oxidation state is not shown by Mn .

Question 11

The pair of lanthanoid ions which are diamagnetic is

Accepted Answer

Magnetic moment = n(n+2) n number of unpaired electron Hence Ce ^ 4+ and Yb ^ 2+ are only diamagnetic.

Question 12

The E ^ value for the Mn ^ 3+ / Mn ^ 2+ couple is more positive than that of Cr ^ 3+ / Cr ^ 2+ or Fe ^ 3+ / Fe ^ 2+ due to change of

Accepted Answer

E _ Mn ^ 3+ / Mn ^ 2+ ^ E _ Cr ^ 3+ / Cr ^ 2+ ^ or E _ Fe ^ 3+ / Fe ^ 2+ ^ Electronic configuration of Mn ^ 3+ =[ Ar ] 3 d^4 Electronic configuration of Mn ^ 2+ =[ Ar ] 3 d^5 Electronic configuration of Cr ^ 3+ =[ Ar ] 3 d^3 Electronic configuration of Cr ^ 2+ =[ Ar ] 3 d^4 As Mn ^ 3+ from d^4 configuration goes to more stable d^5 configuration (Half filled), due to more exchange energy in d^5 configuration.

Question 13

During the preparation of Mohr's salt solution (Ferrous ammonium sulphate), which of the following acid is added to prevent hydrolysis of Fe ^ 2+ ion?

Accepted Answer

During the preparation of Mohr's salt, dilute sulphuric acid is added to prevent the hydrolysis of Fe ^ 2+ ion.

Question 14

'Spin only' magnetic moment is same for which of the following ions? A. Ti ^ 3+ B. Cr ^ 2+ C. Mn ^ 2+ D. Fe ^ 2+ E. Sc ^ 3+ Choose the most appropriate answer from the options given below.

Accepted Answer

array lcc Ions & No. of unpaired electrons & Configuration \ Ti ^ 3+ & 1 & 3 d^1 \ Cr ^ 2+ & 4 & 3 d^4 \ Mn ^ 2+ & 5 & 3 d^5 \ Fe ^ 2+ & 4 & 3 d^6 \ Sc ^ 3+ & 0 & 3 d^0 array Spin only magnetic moment is given by n(n+2) BM Cr ^ 2+ and Fe ^ 2+ will have same spin only magnetic moment.

d and f Block Elements — Previous Year Questions & Solutions