d and f Block Elements — CBSE Class 12 board PYQs

Transition metals are known to form interstitial compounds. The formation of interstitial compounds makes the transition metal:

Assertion (A): Zr and Hf have almost similar atomic radii.
Reason (R): This is due to lanthanoid contraction.

Which of the following ions has the electronic configuration 3d${}^6$? (Atomic numbers: Mn = 25, Co = 27, Ni = 28)

Which property of transition metals enables them to behave as catalysts?

Out of the following transition elements, the maximum number of oxidation states is shown by:

What is lanthanoid contraction?

What is meant by 'lanthanoid contraction'?

Write the outer electronic configuration of the Cr atom (Z = 24).

Which property of the transition elements makes them good catalysts?

Why is Ce⁴⁺ in aqueous solution a good oxidising agent?

Which is more basic, La(OH)${}_3$ or Lu(OH)${}_3$? Why?

What is the effect of increasing pH on a K${}_2$Cr${}_2$O${}_7$ solution?

Why is the third ionisation energy of manganese (Z = 25) unexpectedly high?

Write the atomic number of the element in which the filling of the 3d subshell just starts.

Name the lanthanoid element which exhibits a +4 oxidation state besides the +3 oxidation state.

In a transition series, with an increase in atomic number the atomic radius does not change very much. Why is it so?

What is the difference between the electronic configurations of lanthanoids and actinoids?

Why do Zr and Hf exhibit similar properties?

Why is it that an orange solution of K${}_2$Cr${}_2$O${}_7$ turns yellow on adding NaOH to it?

State the common characteristic of actinoids and lanthanoids which places them in the f-block of elements.

Which is the most stable oxidation state among the lanthanoids?

State a consequence of the lanthanoid contraction shown by the transition elements.

Name one ore each of manganese and chromium.

a) Write any two consequences of lanthanoid contraction.
b) Name the element of the 3d series which exhibits the largest number of oxidation states. Give a reason.

Give reasons for the following statements:
a) Scandium (Z = 21) is a transition element but Zn (Z = 30) is not.
b) [Ti(H₂O)₆]³⁺ is coloured while [Sc(H₂O)₆]³⁺ is colourless.
c) The physical and chemical properties of the 4d and 5d series of transition elements are more similar th …

When MnO₂ is fused with KOH in the presence of KNO₃ as an oxidising agent, it gives a dark green compound (A). Compound (A) disproportionates in acidic solution to give a purple compound (B). An alkaline solution of compound (B) oxidises KI to compound (C), whereas an acidified s …

Give reasons for the following:
(i) Transition elements and their compounds act as catalysts.
(ii) The E° value for Mn²⁺/Mn is negative whereas for Cu²⁺/Cu it is positive.
(iii) Actinoids show irregularities in their electronic configurations.

Complete and balance the following chemical equations:
(a) Fe²⁺ + MnO₄⁻ + H⁺ →
(b) MnO₄⁻ + H₂O + I⁻ →

Give reasons:
(a) The E° value for the Mn³⁺/Mn²⁺ couple is much more positive than that for Fe³⁺/Fe²⁺.
(b) Iron has a higher enthalpy of atomisation than copper.
(c) Sc³⁺ is colourless in aqueous solution whereas Ti³⁺ is coloured.

When chromite ore, FeCr₂O₄, is fused with NaOH in the presence of air, a yellow compound (A) is obtained, which on acidification with dilute sulphuric acid gives compound (B). Compound (B) on reaction with KCl forms an orange crystalline compound (C).
i) Write the formulae of com …

Complete the following chemical equations:
i) 8MnO₄⁻ + 3S₂O₃²⁻ + H₂O →
ii) Cr₂O₇²⁻ + 3Sn²⁺ + 14H⁺ →

Give reasons:
i) Mn shows the highest oxidation state of +7 with oxygen, but with fluorine it shows a highest oxidation state of only +4.
ii) Transition metals show variable oxidation states.
iii) Actinoids show irregularities in their electronic configurations.

What are transition elements? Write two characteristics of the transition elements.

How would you account for the following?
i) Actinoid contraction is greater than lanthanoid contraction.
ii) Transition metals form coloured compounds.

How would you account for the following?
i) Cr²⁺ is reducing in nature while, with the same d-orbital configuration (d⁴), Mn³⁺ is an oxidising agent.
ii) In a transition series of metals, the metal which exhibits the greatest number of oxidation states occurs in the middle of the …

Complete the following chemical equations:
i) MnO₄⁻(aq) + S₂O₃²⁻(aq) + H₂O(l) →
ii) Cr₂O₇²⁻(aq) + Fe²⁺(aq) + H⁺(aq) →

State reasons for the following:
i) Cu(+1) ion is not stable in aqueous solution.
ii) Unlike Cr³⁺, Mn²⁺, Fe³⁺ and the subsequent other M²⁺ ions of the 3d series, the 4d and 5d series metals generally do not form stable cationic species.

Assign reasons for the following:
i) Copper(+1) ion is not known in aqueous solution.
ii) Actinoids exhibit a greater range of oxidation states than lanthanoids.

Complete the following chemical equations:
i) MnO₄⁻ + C₂O₄²⁻ + H⁺ →
ii) KMnO₄ (heated) →
iii) Cr₂O₇²⁻ + H₂S + H⁺ →

Explain the following observations:
i) There is generally an increase in the density of elements from titanium (Z = 22) to copper (Z = 29) in the first series of transition elements.
ii) Transition elements and their compounds are generally found to be good catalysts in chemical …

How would you account for the following?
i) The atomic radii of the metals of the third (5d) series of transition elements are virtually the same as those of the corresponding members of the second (4d) series.
ii) The E° value of the Mn³⁺/Mn²⁺ couple is much more positive than t …

Complete the following chemical equations:
i) MnO₄⁻(aq) + C₂O₄²⁻(aq) + H⁺(aq) →
ii) Cr₂O₇²⁻(aq) + Fe²⁺(aq) + H⁺(aq) →

How would you account for the following?
i) Many of the transition elements and their compounds can act as good catalysts.
ii) The metallic radii of the third (5d) series of transition elements are virtually the same as those of the corresponding members of the second series.
iii …

Compare the relative stability of the +2 oxidation state in aqueous solution for the metals having the outer electronic configurations 3d³4s², 3d⁶4s² and 3d⁵4s².

How would you account for the following situations?
i) The transition metals generally form coloured compounds.
ii) With a 3d⁴ configuration, Cr²⁺ acts as a reducing agent but Mn³⁺ acts as an oxidising agent (Z: Cr = 24, Mn = 25).
iii) The actinoids exhibit a larger number of oxi …

a) Complete the following chemical equations for reactions in aqueous media:
i) Cr₂O₇²⁻ + H⁺ + Fe²⁺ →
ii) MnO₄⁻ + I⁻ + H⁺ →
b) How many unpaired electrons are present in the Mn²⁺ ion (Z of Mn = 25)? How do they influence the magnetic behaviour of Mn²⁺ ions?

Answer the following questions:
i) Which element in the first series of transition elements does not exhibit variable oxidation states, and why?
ii) Why do actinoids, in general, exhibit a greater range of oxidation states than the lanthanoids?

Explain any one of the following statements:
i) The transition metals are well known for the formation of interstitial compounds.
ii) The largest number of oxidation states is exhibited by manganese in the first series of transition elements.

How would you account for the following?
i) The transition elements have high enthalpies of atomisation.
ii) The transition metals and their compounds are found to be good catalysts in many processes.

How is the variability in oxidation states of the transition elements different from that of the non-transition elements? Illustrate with examples.

What is meant by lanthanoid contraction? State one use each of lanthanoid metals and of their oxides.

What is mischmetal? Mention two of its important uses.

Why is the +2 oxidation state of manganese quite stable, while the same is not true for iron? [Z: Mn = 25, Fe = 26]

Write chemical equations for the reactions involved in the manufacture of potassium permanganate from pyrolusite ore.

a) Write the electronic configuration of the element with atomic number 102.
b) What is lanthanoid contraction? What is its effect on the chemistry of the elements which follow the lanthanoids?

The electrode potential values E° (M²⁺/M) for some first-row transition elements are given below:

Explain the irregularities in these values on the basis of …

Describe the steps involved in the preparation of either potassium dichromate from sodium chromate or potassium permanganate from manganese dioxide.

Identify the first-row transition metal ions which have outer electronic configurations of 3d⁴ and 3d⁶, and describe their oxidation states.

The outer electronic configurations of atoms of two members of the lanthanoid series are given below:
i) 4f¹5d¹6s²
ii) 4f⁷5d⁰6s²
Find their atomic numbers. What oxidation states will possibly be exhibited by these elements?

Give a reason for each of the following:
i) The size of trivalent lanthanoid cations decreases with increase in atomic number.
ii) Transition-metal fluorides are ionic in nature, whereas bromides and chlorides are usually covalent.
iii) The chemistry of all the lanthanoids is qui …

a) Name two properties of the central metal ion which enable it to form stable complex entities.
b) Account for the following: zinc salts are white while Cu²⁺ salts are coloured (Z: Zn = 30, Cu = 29).

The outer electronic configurations of two transition metals are (i) 3d⁵4s² and (ii) 3d⁶4s² respectively. From this information predict the relative stability of the +2 and +3 oxidation states of these metals. Which of the two exhibits the larger number of oxidation states?

Write balanced equations to represent what happens when:
i) acidified KMnO${}_4$ solution reacts with iron(II) ions
ii) pyrolusite is fused with KOH in the presence of air

Explain the following observations:
a) The elements of the d-series exhibit a larger number of oxidation states than the elements of the f-series.
b) Cu⁺ salts are colourless while Cu²⁺ salts are coloured (Z of Cu = 29).

How do you account for the following?
i) All scandium salts are white.
ii) The first ionisation energies of the 5d transition elements are higher than those of the 3d and 4d transition elements in their respective groups.

Discuss the general characteristics of the 3d series of transition elements with special reference to their:
i) atomic sizes
ii) enthalpies of atomisation
iii) tendency for complex formation

Explain the following, giving reasons:
i) It is difficult to separate lanthanoid elements in the pure state.
ii) The transition elements form interstitial compounds.

With the help of ionic equations describe what happens when:
i) the pH of a solution of dichromate ions is raised
ii) potassium manganate is electrolytically oxidised

Explain why:
i) E° for the Mn³⁺/Mn²⁺ couple is more positive than that for Fe³⁺/Fe²⁺ (Z: Mn = 25, Fe = 26)
ii) Ce³⁺ can be easily oxidised to Ce⁴⁺ (Z of Ce = 58)

Mention the direct consequence of the following factors on the chemical behaviour of the transition elements:
i) They have incompletely filled d-orbitals in the ground state or in one of their oxidised states.
ii) They contribute more valence electrons per atom in the formation o …

Write balanced ionic equations for what happens when:
i) acidified potassium permanganate solution is treated with oxalate ion
ii) iodide ion is treated with acidified dichromate ion

a) Give one example each of an amphoteric and an acidic oxide of transition metals.
b) Describe the trends in the following cases:
i) melting points of elements in the 3d transition series
ii) atomic sizes of elements in the 4f inner transition series

The sums of the first and second, and of the third and fourth ionisation energies of nickel and platinum are:

i) Give the most common oxidation state of Ni and of Pt, with reason.
ii) Name t …

Complete the following equation:

(a) A transition element X has the electronic configuration [Ar]4s²3d³. Predict its likely oxidation states.

(a) Account for the following:
i) Copper(I) compounds are white whereas copper(II) compounds are coloured.
ii) Chromates change their colour when kept in an acidic solution.
iii) Zn, Cd and Hg are considered d-block elements but not transition elements.
(b) Calculate the spin-onl …

(a) Give three points of difference between lanthanoids and actinoids.
(b) Give a reason and select the one atom/ion which will exhibit the asked property:
i) Sc³⁺ or Cr³⁺ (exhibits diamagnetic behaviour)
ii) Cr or Cu (high melting and boiling point)

(a) Account for the following:
i) Transition metals show variable oxidation states.
ii) Zn, Cd and Hg are soft metals.
iii) The E° value for the Mn³⁺/Mn²⁺ couple is highly positive (+1.57 V) as compared to Cr³⁺/Cr²⁺.
(b) Write one similarity and one difference between the chemist …

(a) The following are transition metal ions of the 3d series:
Ti⁴⁺, V²⁺, Mn³⁺, Cr³⁺
(Atomic numbers: Ti = 22, V = 23, Mn = 25, Cr = 24)
Answer the following:
i) Which ion is most stable in aqueous solution, and why?
ii) Which ion is a strong oxidising agent, and why?
iii) Which i …

a) Account for the following:
i) Mn shows the highest oxidation state of +7 with oxygen but with fluorine it shows a highest oxidation state of +4.
ii) Zirconium and hafnium exhibit similar properties.
iii) Transition metals act as catalysts.
b) Complete the following equations: …

The elements of the 3d transition series are given as:
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Answer the following:
i) Write the element which is not regarded as a transition element. Give a reason.
ii) Which element has the highest melting point?
iii) Write the element which can show an o …

a) Complete the following chemical equations:
i) MnO₄⁻(aq) + S₂O₃²⁻(aq) + H₂O(l) →
ii) Cr₂O₇²⁻(aq) + Fe²⁺(aq) + H⁺(aq) →
b) Explain the following observations:
i) La³⁺ (Z = 57) and Lu³⁺ (Z = 71) do not show any colour in solutions.
ii) Among the divalent cations in the first seri …

a) Complete the following chemical equations:
i) Cr₂O₇²⁻(aq) + H₂S(g) + H⁺(aq) →
ii) Cu²⁺(aq) + I⁻(aq) →
b) How would you account for the following?
i) The oxidising power of the oxoanions is in the order VO₂⁺ < Cr₂O₇²⁻ < MnO₄⁻.
ii) The third ionisation enthalpy of manganese (Z = …

a) Complete the following reactions in an aqueous medium:
i) MnO₄⁻ + C₂O₄²⁻ + H⁺ →
ii) Cr₂O₇²⁻ + H₂S + H⁺ →
b) How would you account for the following?
i) Metal–metal bonding is more extensive in the 4d and 5d series of transition elements than in the 3d series.
ii) Mn(+3) underg …

a) Complete the following chemical equations:
i) Fe³⁺ + I⁻ →
ii) CrO₄²⁻ + H⁺ →
b) Explain the following:
i) Copper(+1) ion is not stable in an aqueous solution.
ii) With the same d⁴ configuration, Cr(+2) is a reducing agent whereas Mn(+3) is an oxidising agent.
iii) Transition me …

Complete the following chemical equations for reactions:
a) i) MnO₄⁻(aq) + S₂O₃²⁻(aq) + H₂O(l) →
ii) Cr₂O₇²⁻(aq) + H₂S(g) + H⁺(aq) →
b) Give an explanation for each of the following observations:
i) The gradual decrease in size (actinoid contraction) from left to right is greater …

a) Complete the following chemical reaction equations:
i) MnO₄⁻(aq) + C₂O₄²⁻(aq) + H⁺(aq) →
ii) Cr₂O₇²⁻(aq) + Fe²⁺(aq) + H⁺(aq) →
b) Explain the following observations about the transition/inner-transition elements:
i) There is in general an increase in the density of elements fr …

a) Write the steps involved in the preparation of:
i) K₂Cr₂O₇ from Na₂CrO₄
ii) KMnO₄ from K₂MnO₄
b) What is meant by lanthanoid contraction? What effect does it have on the chemistry of the elements which follow the lanthanoids?

a) Describe the general trends in the following properties of the first series of transition elements:
i) stability of the +2 oxidation state
ii) formation of oxometal ions
b) Assign a reason for each of the following:
i) Transition elements exhibit variable oxidation states.
ii) …

a) Explain why transition elements show variable oxidation states. Write all the possible oxidation states of an element having atomic number 25.
b) Compare the chemistry of the actinoids with that of the lanthanoids in reference to:
i) atomic and ionic sizes
ii) oxidation states