CBSE Class 12 Chemistry The d and f Block Elements Questions

Electronic Configuration of Transition Metal/Ions

The d-block element is called transition metal if it has partly filled d-orbitals in the ground state as well as in its oxidised state.

The general electronic configuration of transition metal is (n–1) d1–10ns1–2. Exceptions in electronic configuration are due to (a) very little engery difference between (n–1) d and ns orbitals and (b) extra stability of half filled and completely filled orbitals in case of Cr and Cu in 3d series.

Cr : Is2 2s2 2p6, 3s2 3p6 4s1 3d5

Cu : Is2 2s2 2p6, 3s2 3p6 4s1 3d10

To write the electronic configuration of Mn+, the electrons are first removed from ns orbital and then from (n - 1) d orbitals of neutral, atom (if required). For example, the electronic configuration of Cu+, Cu2+ and Cr3+ are respectively 3d10 4s°, 3d9 4s° and 3d3 4s°.

The following questions can be answered with the help of above.

(i) Scandium (Z = 21) is a transition element but zinc (Z = 30) is not.

(ii) Copper (Z = 29) and silver (Z = 47) both have fully filled d-orbitals i.e., (n - 1) d10. why are these elements are regarded as transition elements?

(iii) Which of the d-block elements are not regarded as transition elements?

UNDERSTANDING Δ_fus H^θ ‚ Δ_vap H^θ ‚  AND Δ_a H^θ

In transition metals unpaired (n - l)d electrons as well as ns electrons take part in interatomic bonding. Larger the number of unpaired (n - 1) d electrons, the
stronger is the interatomic bonding and large amount of energy is required to overcome the interatomic interaction.

Question. Amongst TiF₆^2–, CoF₆^3–, Cu₂Cl₂ and NiCl₄^2–, whichare the colourless species? (Atomic number of Ti =22, Co = 27, Cu = 29, Ni = 28)
(a) CoF₆^3– and NiCl₄^2–
(b) TiF₆^2– and Cu₂Cl₂
(c) Cu₂Cl₂ and NiCl₄^2–
(d) TiF₆^2– and CoF₆^3–

Answer    B

Question. Which of the statements is not true?
(a) On passing H₂S through acidified K₂Cr₂O₇ solution, a milky colour is observed.
(b) Na₂Cr₂O₇ is preferred over K₂Cr₂O₇  in volumetric analysis.
(c) K₂Cr₂O₇ solution in acidic medium is orange.
(d) K2Cr₂O₇ solution becomes yellow on increasing the pH beyond 7.

Answer    B

Question. K₂Cr₂O₇ on heating with aqueous NaOH gives
(a) Cr₂O₇^2–
(b) Cr(OH)₂
(c) CrO₄^2–
(d) Cr(OH)₃ 

Answer    C

Question. KMnO₄ reacts with oxalic acid according to the equation
2MnO^{4 –} + 5C₂O₄^2– + 16H+ 2Mn²⁺ + 10CO₂ + 8H₂O
Here 20 mL of 0.1 M KMnO₄ is equivalent to
(a) 50 mL of 0.5 M C₂H₂O₄
(b) 20 mL of 0.1 M C₂H₂O₄
(c) 20 mL of 0.5 M C₂H₂O₄
(d) 50 mL of 0.1 M C₂H₂O₄

Answer    D

Question. Which of the following processes does not involve oxidation of iron?
(a) Formation of Fe(CO)₅ from Fe.
(b) Liberation of H₂ from steam by iron at high temperature.
(c) Rusting of iron sheets.
(d) Decolourisation of blue CuSO₄ solution by iron. 

Question. Which of the following statements about the interstitial compounds is incorrect?
(a) They are much harder than the pure metal.
(b) They have higher melting points than the pure metal.
(c) They retain metallic conductivity.
(d) They are chemically reactive. 

Question. Identify the alloy containing a non-metal as a constituent in it.
(a) Invar
(b) Steel
(c) Bell metal
(d) Bronze 

Question. The catalytic activity of transition metals and their compounds is ascribed mainly to
(a) their magnetic behaviour
(b) their unfilled d-orbitals
(c) their ability to adopt variable oxidation states
(d) their chemical reactivity.

Question. Which one of the following does not correctly represent the correct order of the property indicated against it?
(a) Ti < V < Cr < Mn; increasing number of oxidation states
(b) Ti3+ < V3+ < Cr³⁺ < Mn³⁺ : increasing magnetic moment
(c) Ti < V < Cr < Mn : increasing melting points
(d) Ti < V < Mn < Cr : increasing 2nd ionization enthalpy 

Question. Four successive members of the first series of the transition metals are listed below. For which one of them the standard potential (E°M2+/M) value has a positive sign?
(a) Co (Z = 27)
(b) Ni (Z = 28)
(c) Cu (Z = 29)
(d) Fe (Z = 26)

Question. For the four successive transition elements (Cr, Mn,Fe and Co), the stability of +2 oxidation state will be there in which of the following order?
(a) Mn > Fe > Cr > Co
(b) Fe > Mn > Co > Cr
(c) Co > Mn > Fe > Cr
(d) Cr > Mn > Co > Fe
(At. nos. Cr = 24, Mn = 25, Fe = 26, Co = 27) 

Question. Which of the following ions will exhibit colour in aqueous solutions?
(a) La³⁺ (Z = 57)
(b) Ti³⁺ (Z = 22)
(c) Lu³⁺ (Z = 71)
(d) Sc³⁺ (Z = 21) 

Question. Which of the following pairs has the same size?
(a) Fe²⁺, Ni²⁺
(b) Zr⁴⁺, Ti⁴⁺
(c) Zr⁴⁺, Hf⁴⁺
(d) Zn²⁺, Hf⁴⁺ 

Question. Which one of the elements with the following outer orbital configurations may exhibit the largest number of oxidation states?
(a) 3d⁵4s¹
(b) 3d⁵4s²
(c) 3d²4s²
(d) 3d³4s² 

Question. The correct order of decreasing second ionisation enthalpy of Ti(22), V(23), Cr(24) and Mn(25) is
(a) Mn > Cr > Ti > V
(b) Ti > V > Cr > Mn
(c) Cr > Mn > V > Ti
(d) V > Mn > Cr > Ti

Question. In which of the following pairs are both the ions coloured in aqueous solution?
(At. no. : Sc = 21, Ti = 22, Ni = 28, Cu = 29,Co = 27)
(a) Ni²⁺, Cu⁺
(b) Ni²⁺, Ti³⁺
(c) Sc³⁺, Ti³⁺
(d) Sc³⁺, Co²⁺ 

Question. Four successive members of the first row transition elements are listed below with their atomic numbers.
Which one of them is expected to have the highest third ionisation enthalpy?
(a) Vanadium (Z = 23)
(b) Chromium (Z = 24)
(c) Manganese (Z = 25)
(d) Iron (Z = 26) 

Question. The aqueous solution containing which one of the following ions will be colourless?
(Atomic number : Sc = 21, Fe = 26,Ti = 22, Mn = 25)
(a) Sc³⁺
(b) Fe²⁺
(c) Ti³⁺
(d) Mn²⁺ 

Question. Which one of the following characteristics of the transition metals is associated with their catalytic activity?
(a) High enthalpy of atomization
(b) Paramagnetic behaviour
(c) Colour of hydrated ions
(d) Variable oxidation states

Question. The basic character of the transition metal monoxides follows the order
(Atomic no’s. Ti = 22, V = 23, Cr = 24, Fe = 26)
(a) VO > CrO > TiO > FeO
(b) CrO > VO > FeO > TiO
(c) TiO > FeO > VO > CrO
(d) TiO > VO > CrO > FeO 

Question. Which of the following shows maximum number of oxidation states?
(a) Cr
(b) Fe
(c) Mn
(d) V  

Please refer to the link below for CBSE Class 12 Chemistry The d and f Block Elements Questions